- move all mu4e startup functions to mu4e-utils
- add `mu4e' function to mu4e.el that call these mu4e-utils function
- now easy to start mu4e without showing ui
- mu4e~proc-is-running moved to mu4e-proc
- made mu4e-read-option a bit smarter
- renamed some more functions from mu4e- => mu4e~ (i.e.., mark them private)