Support multiline, comments-as-whitespace, and variable fontification.

Multiline requires expanding the fontification region to include
adjacent lines connected by 'dangling operators'.

Comments must be treated as whitespace in regular expressions to
prevent inline comments from confusing matching.  This includes
end-of-line "//" comments, which can confuse multiline support.

Variable names now use font-lock-variable-name-face where they are declared,
include definition as function parameters, using ":=", and using "var".

TODO: multi-line 'var' support is incomplete.