Exception if yml version not recognised

[jayvdb]

I had version: 0.12.0.dev99999999999999 in my yaml, and it died.

$ moban
Traceback (most recent call last):
  File "/bin/moban", line 11, in <module>
    load_entry_point('moban', 'console_scripts', 'moban')()
  File "/.../moban/main.py", line 33, in main
    handle_moban_file(options)
  File "/.../moban/main.py", line 106, in handle_moban_file
    constants.MESSAGE_FILE_VERSION_NOT_SUPPORTED % version)
TypeError: %d format: a number is required, not str

Very low priority to fix this ;-)
The error should mention that the moban file format version is not recognised, so it is clear that moban is using the version key and nobody else can use it.

[jayvdb]

sortof related ... you can see on coala/coala-bears#2134 that I am avoiding creating a second YAML file, however this means that the version: .. for the file format conflicts with some of the templates (e.g. conf.py.jj2 which expect version is something else.

Perhaps moban could look for _version first, and use it, or use another more _-prefixed descriptive key, for its file format version.