Modernize
Exclude cmd/pt directory from gitignore.
Moved main.go to cmd directory.
Do not use self for receiver name.
Moved search subpackage to pt package.
Moved file subpackage to pt package.
Moved find subpackage to pt package.
Fixed a wrong test.
Removed import itself.
Moved grep subpackage to pt package.
Fixed wrong tests.
Moved ignore subpackage to pt package.
Moved match subpackage to pt package.
Moved print subpackage to pt package.
Moved option subpackage to pt package.
Moved option pattern package to pt package.
Use package alias name.
Use iota.
Updated README.
Updated README.