Merges and rework

[joelpt]

I have largely reworked the google-code-issues-migrator script, inheriting many improvements from the several existing forks out there. Notably:

• Changed from BeautifulSoup to using Google Code Project Hosting API python library.
• Migrates issues, labels, and comments. Safe for repeat runs (won't create duplicate comments or issues).
• Markdown-flavored text written into issues and comments instead of HTML tags.
• Avoid Github API Rate Limit errors by performing 0.5 requests/second.
• Simplified command line parameters.
• Cleaned up README.
• Styled Python code per PEP-8 style guide.