usql v0.5.0

Compatibility fixes! Now almost equal to psql for the major features (variables, passwords, etc), and some major code organization/documentation overhauls. Included in this release:

• Variables working
• Parameters to backslash commands now correctly evaluated
• Added \password command (for PostgreSQL, MySQL, Oracle, and SQL Server drivers)
• Added \set, \unset, \prompt commands for working with variables
• Fixed \gset and \gexec commands
• Fixed \! command
• Added -1 / --single-transaction command line option
• Added \begin, \commit and \rollback commands for working with transactions
• Fixed logic for ~ in paths
• Added support for a .usqlpass file, similar to PostgreSQL's .pgpass. Please see contrib/usqlpass for example file
• Various code and documentation cleanup
• Minor logic/bug fixes for command execution

Plus more. Stay tuned for more -- Google Spanner is coming Very Soon™