Add bibtex-mode snippets

[wynro]

Not much else to say. If there is any problems just ask

[npostavs]

The ((yas-indent-line 0)) setting looks a bit odd to me. I would probably write nil rather than 0 to disable. Is bibtex-mode's indent function unhelpful? Perhaps it should be disabled for the mode globally in a .yas-setup.el file rather than per-snippet, similar to how it's done for python-mode:

yasnippet-snippets/snippets/python-mode/.yas-setup.el

Lines 38 to 39 in b42c2b6

	(add-hook 'python-mode-hook
	'(lambda () (set (make-local-variable 'yas-indent-line) 'fixed)))

[wynro]

As far as I know, the default bibtex-mode doesn't even have indentation. The <tab> is binded to a movement function, and the function indentation-according-to-mode simply puts everything in the first line. The indentation is more an stylistical choice, and to aid visualization. If I don't put it, yasnippet defaults to indent the snippet, and aligns everything to the first line.

About not putting it in .yas-setup.el, I simply didn't knew about the file. Putting 0 instead of the idiomatic nil is also related with my newbiness. I'll do both changes and push again. ¿It's better if I merge it with the other commit, or do you prefer them separated?

[npostavs]

¿It's better if I merge it with the other commit, or do you prefer them separated?

I defer to @AndreaCrotti on that, but I guess it's easier to squash than unsquash.

[AndreaCrotti]

Here I am sorry @wynro
I don't mind either way, but feel free to squash into a single commit since it's just one logical change anyway