Update README.markdown

Fixed formatting and added date for 1.2.0 release.
Update pgx
Release 1.2.1
More specific .gitignore for binary
Fix new migration short name
Release 1.2.2
Update github.com/JackC to github.com/jackc
Ignore tmp dir
Upgrade to latest version of pgx

This allows us to use host for host or unix domain socket instead of
needing the host and socket keys.
Release 1.3.0