Changes:
- Move InvalidListRepliesPolicyError, InvalidTimelineCategory,
InvalidStatusVisibility and InvalidStatusContentTypeError type to the
model package.
- Clean up some code in regards to the parsing of the Enum types.
- Clean up the error messages sent back to the user.
- Use colons instead of semicolons when unwrapping error messages.
- Print errors to Standard Error (os.Stderr)
Allow users to post a status from a file using the --from-file flag.
If both --content and --from-file flags are used then the --content
flag takes precedence.