Merge pull request #10 from phunehehe/installation-instructions

change styling, reword some parts

use markdown for installation instruction

Added authors info, and removed duplicated code

Add link to original gpg-mailgate googlecode.

Enable encryption for signed messages.

Add keymap_only configuration, to ignore public_keys list.

Remove the encrypted to addrs, since that was gpg-mailgate-specific and is no longer used.

Update README file.

Add addendum detailing how to create a dedicated user for gpg-mailgate public keys.

Add description in configuration file of each setting.

Use correct content transfer encoding (7bit).

Don't encrypt if it's a signed message, since that would mess with the signature.

Remove useless domains configuration setting.

Remove attachment content filter because it seems to make PGP-encrypted data invalid.