Summary for multiple files

[tejasbubane]

It would be great if the CLI gave a summary when it is run over multiple data files. Currently it just prints one line (<filename> valid) for each file.

Something like the test runners do:

Analysed 30 files. 28 valid. 2 invalid.

[epoberezkin]

@tejasbubane It should be a major version change, can be done together with the upgrade for ajv v5.0.0.

If you do a PR, please base it on v2.0.0 branch (and PR should be submitted to this branch as well).

Also, it should be supported for all commands (compile, validate and test) and there should be an option to disable this summary.