set \bibhang to \parindent

MLA format requires that the hanging indent of citations be 0.5in. This is not the default in biblatex-mla. This commit sets \bibhang appropriately.
Fix missing parentheses

Fixes issue as reported at https://github.com/jmclawson/biblatex-mla/issues/5
Merge pull request #2 from kc9jud/master

Fixes to conform to MLA standards