`edit` command should accept both full file names and filenames without extension

[Lex-2008]

typical situation:

user@hostname:~/blog$ ls
blog-post.html
blog-post.md

Typing lazyblog edit b<TAB> will lead to this situation:

user@hostname:~/blog$ lazyblog edit blog-post.

Currently, you have to type md manually.

Instead, lazyblog should recognise above situation (user-provided filename ends with dot, such file does not exist, but if you add md - file exists) and add md automatically