v1.0.0 2015-08-18; exec preferred over env.

• aws-keychain exec <name> <cmd ...> added in #10
  • Use this instead of aws-keychain use etc to keep credentials off disk.
• aws-keychain rm secure credential file deletion in #11
• Zsh completion in 011a2a5
• aws-keychain add <name> interactive prompt in #9
• Updated credential file format in #7
• aws-keychain env deprecated in favor of aws-keychain exec.