This means functions shadow variables with the same name, but at least
that's better than listing functions with the documentation from the
variable! (That happened because the call to yas--document-symbols in
snippet-reference.org was prefering function values to variables, while
the yas--document-symbol was prefering variable doc to function doc).
The docstrings for yas-expand and yas-expand-from-keymap are generated
on the fly, depending on how they are called ("context"). Add a context
argument to the synthesizing functions and pass it nil when extracting
docstrings for the manual.
