Bunch of changes in preparation for 0.4.0

- standardize on call(object) interface
- make mime_type available with their short names
- use separate members_rel for collections, instead of profile_rel
- use {src} and {dest} for rel template
- lock rspec to 2.99 (3.0 stack overflows)
- lock mutant to 0.5.12 (more recent is currenlty too slow or hangs)
Prepare v0.4.0