Grepme

- show images in a message

- add caching for messages
- various style improvements

- speed up startup time by using urllib3 instead of requests

- fix import error preventing users from using grepme

- add requirements to git
- add travis CI
- update dependencies; don't use requirements.txt

- refactor lots of code so it can be tested more easily, add tests, document tests in readme
- rename 'text' to 'regex' in usage message
- fix lots of style and refactoring issues
- use DOTALL in regex; now newlines won't stop highlighting. see 15
- make error messages easier to read
- other minor bugs