[Fix #419] Revise running gpg-agent detection
Use the default gpg-agent-info path
Rewrite the gpg-agent module
Rename module gpg-agent to gpg
Disable GPG GUI prompts during SSH connections
Merge branch 'gpg' of https://github.com/sorin-ionescu/prezto

Conflicts:
	modules/gpg-agent/README.md
	modules/gpg-agent/init.zsh
switch to try the new `gpg` module