distinguish between From: and Sender: address

this reverts to the default post-receive hooks.envelopesender behavior while keeping flexibility with the From: address. in some email-environments, setting an explicit (static) envelope sender email is needed.
Allow a static From-address

A static, full From-address ("Name <user@domain.com>") can be specified hooks.fromaddress. if not set, the address is constructed through the $REMOTE_USER enviornment variable and hooks.defaultdomain
Update README.md
Switch to UTF-8

allows accented characters in names and commit messages.
Merge pull request #1 from heldchen/master

Minor fixes and enhancements