pypyr.steps.pathcheck & deprecate multi-input fetches

[yaythomas]

• The new pypyr.steps.pathcheck step allows you see if a path exists on the filesystem. It supports literal paths and glob expansions. It writes handy values into pathCheckOutwith bool for existence and count of files found for the given path. pypyr.steps.fileexists #114
• deprecate old style multi context inputs for fetchjson and fetchyaml, fetchjson and fetchyaml context config to dict #118. this is not just arbitrary: reason is when step is used multiple times in same pipeline, it becomes easy to have left-over values from previous step run left in context that then cause surprising behaviour with the downstream step. the old style is still supported by virtue of pypyr creating the new style inputs under the hood if it finds the old style arguments - but you can expect this to go away by the next major release.
• add info output logging to envget