change incanter.core to a consistent style

Hello there,
I went through Incanter.core's code, and did some cleaning up.

It mostly consists of changing the docstrings to a consistent format, see #204
but I also changed indentation: converted tabs to spaces,
tried to properly indent forms, removed trailing parentheses when they were on a single line,
split extra long lines, etc.

I'm sure I missed some things.
I made no changes to the functionality of the code.

Please tell me whether you would prefer smaller commits.
I would appreciate any feedback, criticism, or guidance.

I plan to go through the rest of the modules, too.