Ntfy

* termux backend
* ruamel.yaml > 0.15 support

- readds pyobc dependency on macosx
- fix homedir ~ substitution
- doesn't throw errors if $WINDOWID isn't set
- escape & in linux notifications"

- Disable PyObjC dep to allow install on MacOS 10.12
- use `yaml.safe_load` to avoid warnings.

- Instapush support (giuseongit)
- Slack support (juanpabloaj)
- Prowl support (sambrightman)
- Syslog support (jlesage)
- MacOS & shell-integration bugfixes (eykd)

- Simplepush backend (tymm)
- Fix `ntfy done --pid` regression (AilisObrian)
- Allow specifying title per-backend in the config
- Notifico! support (eightnoteight)
- Fix bug with homedir shortening (eightnoteight)
- Disable homedir shortening on Windows (avamsi)
- internal cleanup (avamsi)
- add missing PyObjC dependency for MacOS (dcoeurjo)