Fixes #825

* Add support to save file with no extension

The support introduced for files with no file extension is only partial as trying to save the config file would fail with `<file name> requires valid extension`
This adds support to saving such files

* Update gorilla dependency

* Run go mod tidy

* add parsing for stringToString flags

* add logic to return flags default if not val set, add a test

* extract parsing into single func

* add a few more cases

* return nil if unable to parse instead of panicing

* return map[string]interface in order to work with cast.ToStringMap

* mostly copy pflags implementation of the conversion to a stringtostring

- Don't expand user home directory for variable names that simply have a
  HOME prefix;
- Support expansion of variables not followed by the path separator.