Close empty pairs smartly

[shirohana]

I often leave one space in a empty braces in several language.

In old case when I typing: ( _ as <SPACE>)

input: {_}|

And the result:

output: {__}|

I need to delete the extra space by hand, so I made some change.
Now it works like:

// Useful with GitHub markdown
input: [_]|
output: [_]|

input: [__]|
output: [__]|

input: {_foo: bar}|
output: {_foo: bar_}|

[shirohana]

Excuse me (´・ω・｀)？

[shirohana]

I rebased my commit to jiangmiao:master, would you merge my pull request?

[jiangmiao]

Thank you for your contribution!