Vim syntax: support lifetimes with delimitMate.

When it's a lifetime, a single quotation mark shouldn't have a matching
single quotation mark inserted after it, as delimitMate does by default.

Note that this is not without problems; a char literal coming after an
odd number of lifetime markers will have its quotation marks behave a
little strangely. That, however, is not my fault, but delimitMate's:
https://github.com/Raimondi/delimitMate/issues/135