So, in RST, 'http://google.com.' should be parsed as a link
to 'http://google.com' followed by a period.
The parser is smart enough to recognize balanced parentheses,
as often occur in wikipedia links: 'http://foo.bar/baz_(bam)'.
Also added ()s to RST specialChars, so '(http://google.com)'
will be parsed as a link in parens.
Added test cases.
Resolves Issue #291.