New snippet with selected text

[songjie-dong]

No description provided.

[joaotavora]

See https://github.com/capitaomorte/yasnippet#not-contributing-snippets

[songjie-dong]

Sorry about no description.

This patch is not a snippet, but used in the following scene:

1. recently entered the code suitable for use as snippets
2. select code
3. C-c & C-n to add new snippet
4. new snippet's buffer contain those code
5. modify and save new snippet

A optimization for new snippet action.

[joaotavora]

Ah ok, I'll reopen this and have a look when I find the time. thanks for the description.

[lewang]

@songjie-dong Please add your description to the actual git commit messages. Github may not be around with this project forever, it's important to have meaningful commit messages.

[songjie-dong]

I've already added comment, @lewang thanks for your reminding.

[npostavs]

I've rebased this as #698.