Added as and move keywords to Vim syntax file

[netvl]

as (already for a long time) and move (which was only added recently, AFAIK) are not marked as keywords in Vim syntax file, so they are not highlighted as keywords in Rust sources. This PR fixes this.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

[steveklabnik]

Move has been a keyword for a long time, but it was removed in 0.6, and kept reserved. Then it was recently brought back.=

[netvl]

@steveklabnik, didn't know that. Anyway, previously it wasn't used so its missing highlighting wasn't a problem. as, however, is a [frequently] used keyword for a long time, but for some reason it still wasn't marked as such in Vim syntax file.

[ftxqxd]

as is already a rustOperator (see line 17), so marking it as a keyword as well is unnecessary. as is already highlighted in Vim today.

[tomjakubowski]

Could you squeeze in an update to rustFail "\<fail\(\w\)*!" contained for panic! too?

[netvl]

@P1start, strange, it is not highlighted for me. Probably my color scheme problems, I'll revert it.
As for panic!(), sure, I'll do it.

[netvl]

Ah, I see that since as is deemed an operator it is highlighted as such and operators in my color scheme do not have a particular highlighting. Never thought of as as an operator though >_<
Anyway, I fixed everything and also rewrote fail to panic.

[cuviper]

@netvl, did you consider rustStorage for move? That's what I chose in #18789. Then it will be highlighted the same way as ref, mut, and the & sigil, for instance, all mapping to vim's StorageClass. If you agree, I can rebase my pull request to change where you put it. :)

[netvl]

@cuviper, no, I didn't. Either would be fine for me, as long as they are highlighted :)