Make unicode-grep tool measure line length with UTF8.size

Also don't claim to be checking for last lines without newlines as use
of TextIO.inputLine precludes this.

Extend unicode-grep to check for more style violations

Now has four tests:
- TABs
- trailing whitespace
- unicode
- line length > 80

Internal documentation notwithstanding, this doesn't currently scan for
missing newline on last line because TextIO.inputLine masks that.

Will rename to hollint or similar in subsequent commit.

The current regression test sequence has the line length test turned
off, but I am keen to turn that on soon.