replace whitespace/forbidden characters in branch name on feature start

[e110c0]

many projects expect the name of a branch to include the ticket number and a short title. To be able to just c&p the ticket title into the feature: start input, it would be nice if any whitespace and forbidden characters would be exchanged automatically (e.g. with _).

example:
"27 my fancy feature" => "27_my_fancy_feature"

[devmanny]

I sent a pull request to solve this, I am waiting for it to be approved

#29

[vector-of-bool]

Closed by merge of #29