Add a commandline utility

[asdf-format]

Add a commandline utility

[drdavella]

This currently exists for all but validate.

[drdavella]

@perrygreenfield and @nden, do we know what was intended by the validate command line tool? Files are automatically validated when they are opened. Is the point just to return whether or not a given file is well-formed ASDF or not?

[nden]

My guess, given the date of the issue, is that the code has evolved and this is not needed any more.

[drdavella]

Okay, that seems reasonable. It would also be very easy to provide a simple yes/no interface to indicate whether a file is valid or not. Although in the case that a file was not valid, you'd probably want to know why...

[drdavella]

Closing since a command line utility already exists. If a validation feature is specifically requested, we can open a new issue.