Add fstab syntax definitions

[flopp]

This commit adds simple syntax definitions for fstab files.

[sharkdp]

Awesome, thank you very much!

Works great for me:

Two questions:

• Since we "understand" which field is which, it would be great if we could highlight the <type> and the <options> fields in different colors. Maybe even separate colors for the two filepaths/UUIDS. I know it's hard to choose appropriate scopes (http://www.sublimetext.com/docs/3/scope_naming.html), but it would be a great visual aid to parse the file quickly. As a bonus, we could even parse the comma-separated options-string and highlight known keywords.
• I think we could also match on mtab (/etc/mtab), as it seems to have the same syntax. Not completely sure on that, though.

[eth-p]

I agree with @sharkdp. It would be a great visual aid to have different colors for <type> and for each field in <options>.

[eth-p]

@flopp @sharkdp: How about this for colors? I tried to base it off of the scheme in #698.

I forked @flopp's branch and edited the syntax file in eth-p@f7ede0d to come up with that. If you like it, you can merge it back into this PR.

[sharkdp]

@eth-p looks great.

[flopp]

@eth-p good job. I like it!

[eth-p]

Great! I'll merge this PR and open a new one for the added colors.

[sharkdp]

This has been released in bat 0.13.