Improved docs

[Mnenmenth]

closes #11

• This adds more documentation to the entire project and refactors any existing documentation to be in the "java-doc" style

• This also contains a couple small changes that didn't necessarily warrant its own issue/PR

  • Some small changes to logging messages (such as being slightly more descriptive and/or a new line character being added)
  • UpdateableState::update_state() now takes a const reference
  • Class constructors that accept a StateVariables instance for configuration now also take a const reference to the state
  • Remove an unnecessary length parameter from session::do_write, since we can just call msg->length() to get the string length

• [x] #50 should be reviewed and merged before reviewing this