Increase truth of some comments
Detect omitted -directory flag and print an error.
Add a -build option to specify a build command.
This is useful if you need to specify a package name to "go build"
or are using an external build system.
Update README.md

Document the command line options.
Do -directory check before any work is done.
Fix some formatting.
Update README.md

Note that the -command runs inside -directory.
Merge pull request #2 from jimstudt/master

Added flag to specify build command and some minor enhancements.