Get src/n-bit to build given tight-equality

Add MOD_ss to srw_ss()

If it breaks proofs, this is easy to reverse in a script by doing

val _ = diminish_srw_ss ["MOD_ss"]

before the old behaviour is being relied upon

Clean up some code.

Remove the constant bit$LSB, which was simply arithmetic$ODD. This may break some user proofs.

Also tidy-up bitScript and numeral_bitScript.

Overhaul to rich_listTheory (it had become a bit of a disaster area).

Some points:

1. rich_listTheory now uses the same constant names that are used in listTheory, e.g. TAKE instead of FIRSTN.

2. listTheory theorems are no longer replicated (saved again) in rich_listTheory. This avoids DB.match returning multiple instances of the same theorem. It also avoids saving around 100 theorems twice — in some cases after re-proving them.

3. Compatibility is now maintained though a bunch of SML "val" assignments added using adjoin_to_theory, e.g.

val ZIP_FIRSTN_LEQ = ZIP_TAKE_LEQ
val ALL_DISTINCT_SNOC = listTheory.ALL_DISTINCT_SNOC

4. Some incompatibilities are introduced:

* FRONT___LENGTH is deleted, since it is the same as rich_listTheory.LENGTH_FRONT.
* COUNT_LIST___ADD -> COUNT_LIST_ADD
* COUNT_LIST___COUNT -> COUNT_LIST_COUNT
* The compute theorems for COUNT_LIST and SPLITP have been renamed.
* Some other theorems are no longer saved, e.g. rich_listTheory.list_INDUCT

5. Some theorems in listTheory have gained quantifiers.

Adopt ML-style syntax for case expressions and use freed up "||" for bitwise-or. See issue #24.

A few extra theorems.

Added new operations for shifting by a bit-vector value, namely:

LSL: <<~
LSR: >>>~
ASR: >>~
ROR: #>>~
ROL: #<<~

These are supported by the procedures in blastLib. For example, one can prove

w <+ 10w /\ s <+ 3w ==> w <<~ (s + 1w) <+ 73w : word16

The time-complexity is a pretty shocking but "simple" 32-bit problems seem to
be okay. NB. ROR and ROL only bit-blast with word sizes that are a power of
two.

Added a new conversion WORD_MOD_BITS_CONV for mapping applications of
``word_mod w (n2w n)`` into ``(h -- 0) w`` where n is a power of two.

Also added support for bit-blasting arbitrary multiplication, but the word-size
limit is set to 8 bits by default. Things seem to be just about feasible with
that limit (and become horrendously slow after that).

To improve performance, the conversion BBLAST_CONV does not have exactly the
same coverage as before. For backward compatibility, a conversion
EBLAST_CONV (which calls SAT at every bit position) is now available.

Remove Unicode that has crept in to some source scripts.

Fix handling of quantifiers in BBLAST_CONV. For example, was previously
converting ``!a. P a`` to ``!a. P a = T`` instead of ``(!a. P a) = T``.

Few other minor tweaks.

Added a bit-blasting conversion: BBLAST_CONV. This goes beyond the
capabilities of WORD_BIT_EQ_CONV by expanding out additions / subtractions.
This allows the new conversion to automatically handle small but tricky bit
vector goals. For example:

``(x && 3w = 0w:word32) ==> ((x + 4w * y) && 3w = 0w)``

and

``!a:word8. a <+ 4w /\ b <+ a /\ c <=+ 5w ==> (b + c) <=+ 7w``

(These aren't provable with wordsLib.WORD_DECIDE.)

Obviously bit-blasting is a brute force approach, so the new conversion should
be used with care. It will only work well for smallish word sizes and when
there is only and handful of additions around. It is also "eager" -- additions
are expanded out even when not strictly necessary. For example, in

``(a + b) <+ c /\ c <+ d ==> (a + b) <+ d:word32``

the sum ``a + b`` is expanded. Users may be able to achieve speed-ups by first
introducing abbreviations and then proving general forms, e.g.

``x <+ c /\ c <+ d ==> x <+ d:word32``

The conversion handles most operators, however, the following are not covered /
interpreted:

-- Type variables for word lengths, i.e. terms of type ``:'a word``.

-- General multiplication, i.e. ``w1 * w2``. Multiplication by a literal is
okay, although this may introduce many additions.

-- Bit field selections with non-literal bounds, e.g. ``(exp1 -- exp2) w``.

-- Shifting by non-literal amounts, e.g. ``w << exp``.

-- ``n2w exp`` and ``w2n w``. Also w2s, s2w, w2l and l2w.

-- word_div, word_sdiv, word_mod and word_log2.