[Enhancement] Run cfn-guard check without parameters

[benbridts]

Is your feature request related to a problem? Please describe.
Currently you always have to specify both the ruleset and the templates. This makes scanning mulitple templates in one source code repository, or templates across different repositories difficult (see also #22 )

Describe the solution you'd like
Having a default filename for the rules and allowing a list of templates as input, would make it a lot easier to run. eg.

cfn-guard check template1.yaml template2.yaml
cfn-guard check template*.yaml
cfn-guard check --rule_set non-default-rules *.yaml

[ldomb]

Would be great to be able to point to multiple rules as well in the same command.

[benbridts]

Can we reopen this? @shreyasdamle

Not being able to pass multiple files makes it so much harder to integrate this in a repository