Major rewrite of handle() to better facilitate lists within definition list items

The plugin now completely writes its own plugin calls.  Both DT & DD tags use
DOKU_LEXER_ENTER & DOKU_LEXER_EXIT states (rather than the previous DOKU_LEXER_MATCH).
This change allows the plugin to work better with DokuWiki's own EOL & paragraph
handling and avoids invalid html which could occur previously (e.g. when lists where
included within DD items).

PHP class code is also updated to use visibility properties.
Minor changes to improve white-space handling
- ignore any spaces after syntax triggering characters
- include a new line after opening <dl> tag
Update tests to match actual white space behaviour
Rework tests making the code slightly simpler & replacing '\n'
with NL constant.
Merge pull request #1 from Chris--S/tests

Updated Tests
New release.