Improve Purging and Add Algorithms

This release improves the process of purging keyrings by:

• Fixing #57 where keys would not be cleared on logout if the session keyring was misconfigured.
• Adding #67 to always sync the filesystem metadata when purging keys.

Minor features include:

• Adding cryptographic algorithms from the 4.13 kernel (#64)
• Improving our Travis CI processes (#68, #69)

Features coming in 0.3:

• Major Documentation rewrite (#10)
• Commands to automatically handle ext4 feature flags
• UI refactoring