Update old-point in go-eldoc--goto-beginning-of-funcall between iterations

The current behaviour only works because of an unintended side-effect
in go-goto-opening-parenthesis, where it will jump to the beginning of
the buffer if point isn't in a balanced pair of parentheses. Future
versions of go-goto-opening-parenthesis will not move point at all.

With the change to go-goto-opening-parenthesis, the old implementation
of go-eldoc--goto-beginning-of-funcall could end up in an infinite
loop.
use a simple looking-back instead of movement and string matching in go-eldoc--beginning-of-funcall-p
support functions/types with unicode in them
Make type in fundecl optional to support `func foo(a, b int)`
Merge pull request #2 from dominikh/fix/infinite-loop

Update old-point in go-eldoc--goto-beginning-of-funcall between iterations
Merge pull request #3 from dominikh/improve/beginning-of-funcall-p

use a simple looking-back instead of movement and string matching in go-eldoc--beginning-of-funcall-p
Merge pull request #4 from dominikh/fix/unicode

Support identifiers and types with unicode in them
Merge pull request #5 from dominikh/fix/no-type

Make type in fundecl optional to support `func foo(a, b int)`