Tswift

Fixed
- Fix error handling if no lyrics were found in the Metrolyrics API either as a 200 response with
a missing 'lyrics-body-text' element or a 404 response.

Changed
- A base level exception file and class `TswiftError` was added to catch any absent lyrics
from requests made to Metrolyrics.

Fixed
- Fix `AttributeError` due to unmatched regex - Metrolyrics has switched all
links to HTTPS by default.

Changed
- All URLs this package loads use HTTPS by default.

Fixed
- Fix import due to upstream name change (google -> googlesearch)

Fixed
- Fix error caused by HTML comments within song div. Thanks [nizzit][]!

Thanks [a-johnston][]!

Fixed
- Variable names prefixed with underscore when they should convey publicness
- Removed unnecessary `__str__` definitions due to `__repr__` implementations

Added
- Slugify and deslugify
- Song formatting for pretty printing
- Entry point for CLI, `tswift`
- Search for lyrics via the `google` package
- Artist name and song name CLI arguments

Fixed
- Forced UTF-8 encoding to prevent character mangling, thanks
[EsotericAlgorithm][]!

Added
- Simplified API: `Artist.songs` and `Song.lyrics` are now properties that are
loaded on first access, so calling `load()` is no longer necessary.
- Simplified API: `Artist.load()` and `Song.load()` return `self` so that you
can perform further operations.
- Added `repr()` for `Artist`.
- Explicitly added Revised BSD license.