Fixed syntax highlighting of regular expressions

In HTML output, syntax highlighting of regular expressions could become
corrupted.  This patch whitelists "/" as a character with a matching
terminal like '"' and "'" for strings.

See also Ruby Bug #6488 and #6523

Conflicts:
	History.rdoc
Fixed Regexp backreference corruption

Regular expression parsing was switched to use single-quote escaping
rules.  Using double quote rules, extra backslashes and white spaces was
added.

See also Ruby Bug #6488 and #6523
Fixed lexing of character syntax like ?z

Character syntax `?z` was lexed as an integer token `"zz"`.  This has
been fixed to lex as a single character string `"z"`.  While this won't
round-trip, it is acceptable for syntax highlighting.

This was discovered by Xavier Noria (@fxn) in rails/rails#7172.

Conflicts:
	History.rdoc
Fixed parsing of escaped characters in strings
Fixed tokenization of "a%1"

Updated failed tokenization examples to use bad octal digits

Conflicts:
	History.rdoc
	test/test_rdoc_markup_to_html.rb
	test/test_rdoc_markup_to_html_snippet.rb
Gave TkEND_OF_SCRIPT#text a value

This allows __END__ to be shown in HTML verbatim blocks

Conflicts:
	History.rdoc
Tokenize out-of-place reserved words as identifiers
Parse unicode characters above \uFFFF

The regular expression matching identifiers was incomplete for unicode
characters.  Now 𝖒 can be parsed in an identifier.

Ruby Bug #7524
Added limited HEREDOC tokenization

A TkHEREDOC is only generated when the heredoc identifier is followed by
a line end.  When followed by a method call, comma, etc. a TkSTRING is
returned instead so the source output in the HTML view is correct.

Fixes #162

Conflicts:
	History.rdoc
	lib/rdoc/store.rb
Fixed tests broken by incompetent cherry-picking

Since I didn't run tests during cherry pick I missed some merges.  These
have no been corrected.
Set version to 3.12.2

The parser changes to support %i were only bug fixes to master.

As it happens, %i support is by accident and RDoc consideres this a
method call to %.  This should probably be fixed in master at some point.