Add some subscript Unicode characters (+, -, =) to emacs bindings

Fix typo introduced in last commit

Add more subscript letters to the hol-unicode map

Add yet more special Unicode chars to unicode maps in hol-unicode

Some of them may even be memorable

Rationalise handling of Unicode lowercase phi characters

The "mainline" phi character in Unicode is U+03C6, which in most fonts
looks more like what TeX calls a \varphi. In the font you are using to
view this message it is "φ". There is also an additional U+03D5, which
is written the way Knuth wanted his \phi to look (in this font: "ϕ").
If these are seen in HOL input, EmitTeX now maps them appropriately.
Similarly, the Emacs mode for producing them now maps C-S-p h to the
second and C-S-p v to the first.

Add more Greek letters to Emacs hol-unicode.el

Use elisp insert function to send superscript 1, 2 and 3

As with the negation symbol, it seems necessary to explicitly call
insert to get these Unicode characters into one's buffer. In all other
places, simply quoting the string seems enough.

Emacs unicode commands for the word shift operators

Provide support for Unicode subscript 'r'

Thinking that this might be a reasonable annotation for relationScript's
set operators. For example, R1 RUNION R2 might be written R1 ∪ᵣ R2

Provide emacs keybinding for Unicode triangle

Make U+2218 (∘) alternative syntax for combin$o

Also bind C-S-0 0 as Emacs keybinding to generate it.

Add Emacs keybinding for not-iff Unicode char

C-{(,)} bindings for paren maps have to go to C-M-{(,)}

This is because C-) is already taken for the various "things in circles
symbols".

Add some Unicode parentheses to emacs mode

More negated relation symbols for the hol-unicode.el bindings.

Add emacs binding for ≰ symbol in hol-unicode.el

Fix typo in hol-unicode.el

Add a bunch of emacs bindings for Unicode superscript letters.

A couple more Unicode in Emacs bindings.

Add some unicode bindings for the emacs mode (for ⊌ and ⊎)

Add binding for \sim character (U+223C ∼) to emacs unicode file.

Unicode emacs bindings; for \o{times,plus,slash,minus,dot} chars

Three more emacs-mode Unicode characters (superscript +, - and =)

Fix the keybinding for Unicode “less than or equals”.

It turns out that C-Q is not understood to be the same as C-S-q, but
rather just C-q, which had the effect that my binding for ≤ overrode
the standard (and useful) quoted-insert emacs command.

A new keybinding for less-than-or-equals in hol-unicode.

C-Q is not great, but the mnemonic is ‘less than or eQuals’.

Add an Emacs binding ("not 0") for the emptyset symbol.

Emacs key-bindings for fancy Unicode brackets.

More emacs bindings for Unicode (sub and super-scripts mostly)

C-M-_ can be followed by digits to get those digits as subscripts.
Similarly, C-M-^ can be followed by digits to get them as
superscripts.

Emacs key-bindings for Unicode symbols iff and superscript +

Add a couple of emacs keybindings for two forms of right arrow.

Fix handling of special 'U' constant, retaining better backwards compatibility.

In particular, there is now a special form 'univ' that behaves as 'U' did.
Further, with Unicode on, the character U+1D54C is used in the same way.
This character may not be in many fonts, so add another trace to turn its
use off. If you can see it, it's a nice 'double-struck' U. I would have
gone for a script-style U, but it leant over too much, and so overlapped
the following left-paren character.

Add key-bindings to generate capital and lowercase omega characters.

Oops. I also found subscript numerals and cut and pasted them into
this file as a prelude to getting Emacs to emit them somehow. But I'm
not sure quite how just yet. They at least need to be commented out.

I couldn't resist adding pi, phi and psi (and threw in a lower-case
rho as well). These letters aren't as useful as they should be at the
moment because the system barfs if you try to put them into binding
position. I.e., ∀Γ. P(Γ) fails. Actually, it fails for two reasons:
* the lexer reckons that ∀Γ is one symbol, not two. So you have to
write ∀ Γ in order to stop the merge
* and then some annoying code in Parse_support jumps up and down
about Γ being invalid
Both of these are fixable, and on my to-do list at the moment.

More Greek letters, as well as bindings for subset and negation. ('c'
seems reminiscent of the subset shape, and isn't an obvious choice for
any Greek letter I can think of. Likewise 'u' and 'i' for union and
intersection seem pretty safe. (Who wants to write iotas anyway?))
For psi, phi and pi, I may set up C-S-p as a prefix binding, so that
one would type <C-S-p i> to get pi, <C-S-p h> to get phi etc. And
C-S-M-p for the capital versions of these.

Some Emacs key-bindings for Unicode characters of interest.
<control>-! for universal quantification, for example.