Feature - Refactoring Modifiers and Writers

[cnoon]

This PR refactors the Writer and Modifier protocols to include a LogMessage prefix. There are two main reasons for these changes.

1. We wanted to be more explicit with the protocol names to make their intent more clear. The previous names were so vague that they didn't really express intent clearly.
2. We all agreed that Formatter was better than Modifier, but that LogMessageModifier was much better than Formatter. We also agreed that LogMessageModifier was much better than Willow.Formatter everywhere. In the end, we decided that additional verbosity to avoid conflicting with Foundation APIs was probably the best decision.

[EricAppel]

Really like the clarity that these changes bring. 👍🏽

[cnoon]

These changes have been merged into the swift3 branch. I'm going to close this PR out.