Do not advertise the email address as-is

..even though it doesn't look like it's enough for spammers to stay away..
Add THANKS file
Fix #15, add message if .gitignore is fine
Add safe_mode option, auto perform .gitignore check only for selected cmds
Enhance comments and command output
Add "check" command to perform a sanity check on the .gitignore file
Fix missing spaces, output text layout
Behavior change, default config file now created at "gitver init"

- refactoring
- pass loaded configuration instead of importing it
- enhance "gitver init" command help
Fix missing exit if template file couldn't be written
Enhance #18, more comments, refactor, add "preview" command for templates

The "gitver preview <templates>" command will output to stdout instead of
creating the destination file, useful for testing or previewing the result.