Delete unused code in config
Inline encode/decode in config
Reorganize config
Add read method to config type
Deprecate verbose dir value in config
Deprecate Hostname field on configure
Deprecate problems host in config
Use platform independent pathnames
Simplify fetch
Normalize api per golint's suggestions
Delete unused field on problem struct
Normalize handlers per golint's suggestions
Fix pointer in api
Refactor submit command action into handlers/submit

This PR extracts the `submit` command action handler into a stand alone handler
in `handlers/submit.go` to match the other actions.

  * The related specs from `main.go` have been moved to
`submit_test.go`.
  * `Version` and `UserAgent` was moved out of `main` and into
`config` for this update to work. There may be a better place for these
constants / variables.
  * `msgPleaseAuthenticate` is currently duplicated in both `main` and in
  `submit`. Do you have a preferred way to share these messages?