command-line with sub-commands

[reuvenharrison]

Currently the oasdiff cmd-line has many arguments, some of which are incompatible with each-other.
This is a result of a natural evolution from a single-purpose diff tool, through options that were added later, including the addition of two breaking-changes implementations and a future change-log option.

It is time to move to a sub-command design which will simplify the user experience and implementation.
Please see the design document.

Comments are welcome.

[reuvenharrison]

Work on sub-commands is in progress: #293

The new cmd-line will be released as version 2.0.0 and it won't be backward-compatible with the current cmd-line which means that all users will need to update their integration.

Your comments are welcome.