Update docs.html

Fix URL.
Merge pull request #198 from nelsonjchen/patch-1

Update docs.html
Merge remote-tracking branch 'remotes/zaach-original/master'
(re)introducing optional 'easy keyword lexing' a la #63: now only enabled when you specify the lexer `%option easy_keyword_rules` (this means that #63 is no longer tightly coupled with %option flex: the jison lexer behaved like flex by default, until you switch on the `%option easy_keyword_rules`)