Implement formatting-around-cursor feature
Add unit tests for given feature
Format around the cursor while selection is empty
Format computation expressions correctly around the cursor

The original form didn't print out '{' and '}'.

The current form isn't nicely indented. We should look how it is
different with the case where there is a selection.
Prettify results of formatting around cursors

'formatAroundCursor' calls 'formatSelectionFromString' internally since
the latter does some normalization on ranges to make the code parseable.
Merge pull request #91 from dungpa/features/formatting-around-cursors

Formatting around cursors feature