Fixes whitespace inconsistencies.

There is a mix of tabs and spaces, as well as multiple indention styles for the
same content.
Create / remove build directories.
Remove missing source files.
Add negative number parentheses clarification.
Remove trailing whitespace.
Flesh out readme using intro text
Merge pull request #10 from wting/add_readme

Flesh out readme using intro text.
Merge pull request #9 from wting/add_negative_number_clarification

Add negative number clarification.
Merge pull request #8 from wting/fix_makefile

Fix makefile.
Fix typos, add parser
Merge branch 'master' of github.com:w7cook/AoPL
Introduction text to Section 2
Add files that are missing, update makefile to build them
Merge branch 'master' of github.com:w7cook/AoPL
Rename "let" to "var" and call it a variable declaration. Start using parser/unparser more