feat(state): Report general and CAN session state

[epage]

There are two controversial parts of this

• If the interface isn't communication, time_start and time_communicating
  throw an error rather than return 0.
• Each state property will treat fault like any other return code,
  raising an exception or warning, when these properties are accessed

Standard checklist

• This contribution adheres to CONTRIBUTING.md.
• New tests have been created for any new features or regression tests for bugfixes.
• tox successfully runs, including unit tests and style checks (see CONTRIBUTING.md).

[coveralls]

Coverage decreased (-0.1%) to 63.413% when pulling b4ff4e1 on epage:state into 427739f on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.427% when pulling 67b69cd on epage:state into 427739f on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.433% when pulling 93acd1b on epage:state into 427739f on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.428% when pulling 812caf9 on epage:state into 068181e on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.428% when pulling 812caf9 on epage:state into 068181e on ni:master.

[epage]

Originally, each state property would call check_for_error on the fault. After talking with Christian, I switched to an explicit check_fault function.

[coveralls]

Coverage decreased (-0.1%) to 63.428% when pulling 08c3d76 on epage:state into 068181e on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.428% when pulling 08c3d76 on epage:state into 068181e on ni:master.

[coveralls]

Coverage decreased (-0.1%) to 63.428% when pulling 8dd8624 on epage:state into 068181e on ni:master.