vim: Add StrBuf as type to hilighting
Reduce HashMap allocations.
std: Fix demangling with middle special chars

Previously, symbols with rust escape sequences (denoted with dollar signs)
weren't demangled if the escape sequence showed up in the middle. This alters
the printing loop to look through the entire string for dollar characters.
auto merge of #13609 : richo/rust/str-type-vim, r=alexcrichton

It seems really weird to me when StrSlice and str highlight sanely, but StrBuf doesn't.

I think I added it to the right place.
auto merge of #13614 : cgaebel/rust/master, r=brson

We previously allocated 3x for every HashMap creation and resize. This patch reduces it to 1x.
auto merge of #13615 : alexcrichton/rust/improve-demangling, r=brson

Previously, symbols with rust escape sequences (denoted with dollar signs)
weren't demangled if the escape sequence showed up in the middle. This alters
the printing loop to look through the entire string for dollar characters.