Improve code extraction based on #11
Add Mocha to dev dependencies

Before this, the tests wouldn't run if we haven't got Mocha already
installed globally.
Code review on code extraction parser

* Add a JSDoc comment documenting the behavior, expectations and
  parameters.
* Ensure the offset is on the opening brace.
* Reorganize `depth` and `cursor` initialization, so we easily
  understand that the depth increases only when we find an opening brace.
* Consume single line comments directly (optimization) and remove now
  obsolete variables (`bComment` and `lComment`).
* Swallow 2 chars for block comment opening and closing (since the
  opening and closing sequences are 2 chars long) (slight optimization).
* Refactor string matching to make it easier to understand (IMO).
* Fix code style issues: presence of non breaking spaces, missing spaces
  before and after function parentheses and operators.
Fix code style in tests

* Fix funny indent.
* Remove inconsistent spaces sometimes around function arguments.
* Add spaces around function parentheses.
* Fix consistency in string delimiter.
* Replace some funny non-breaking spaces by regular spaces.
Optimization on single line comment and loop continue
Merge remote-tracking branch 'origin/better-extract-code-val' into better-extract-code

* origin/better-extract-code-val:
  Optimization on single line comment and loop continue
  Fix code style in tests
  Code review on code extraction parser
  Add Mocha to dev dependencies
Merge pull request #12 from SassDoc/better-extract-code

Improve code extraction based on #11