Improved type signatures

Main changes compared to v0.1:

• More type signatures added to methods
• Improved README.md

Bugfixes and improved documentation

Main changes compared to v0.1:

• New helper function get_buildid_from_path, this adds a dependency to pyelftools
• Improved documentation, especially regarding errors
• All calls going through ctypes now have explicit argument types
• Bugfixes for path conversions through _create_string_buffer

First release

We're going live!