Add support for explicit file extensions

[eshapard]

Fixes #82
Closes #82

Checklist

• I have made a change to this repository, be it functionality, testing, documentation, spelling, or grammar.
• I updated my branch with the master branch.
• I have added the necessary testing to prove my fix is effective/my feature works (or I did not modify functionality).
• I have added necessary documentation about the functionality in an appropriate .md file.
• I have appropriately commented any code I have modified

Short description of what this PR does:

Allows notes to accept explicit file extensions other than the default in note filenames.

[primis]

Is there a reason here for limiting extensions to 4 characters?

[eshapard]

@primis I figured there should be a limit. Otherwise, If you make a note about Mr.Bojangles, notes would assume that .Bojangles is the file extension.