Support checking multiple files at once

Please support an arbitrary number of files passed in on the commandline. For example:

cfn-lint template1.yaml template2.yaml

[asottile]

Nearly every linter supports as a standard interface linter [filename, [filename ...]] (except this one) please consider the precedents set by tools like pyflakes / flake8 / pylint / eslint / prettier / black / etc.

Not only does this make invocation dead simple with xargs, it is much more performant (the interpreter and subprocess overhead occurs once instead of a linear amount of times by file). This overhead is especially high on windows. (even on Linux, compare the time taken between git ls-files -- '*.py' | xargs pylint vs. git ls-files -- '*.py' | xargs -n1 pylint).

Also in line with other posix tools you could simply invoke with a glob linter *.yaml instead of needing to copy paste a complicated wrapper everywhere.

The main motivation here is so that this linter can easily be integrated into other frameworks, in particular https://pre-commit.com

[kddejong]

Released in v0.7.4