pwm supports notes now

* Added pwm_git_note_get(), pwm_git_note_set() and pwm_git_note_rm()
  to retrieve, set and remove notes from blobs.

* Added pwm_db_note_get(), pwm_db_note_set() and pwm_db_note_del() to
  to retrieve, set and delete encrypted notes from entries.

* Added pwm_gpg_encrypt_armor() to create ASCII armored encryption
  output

* Added pwm_str_read_all() to read until EOF from a file descriptor.

* Added the pwm-note builtin with del, get and set subcommands to
  delete, retrieve and set encrypted notes to passwords.