Manually specifying range length is laborious and error-prone; this
commit adds an argument -end-pos=Line:Column to specify the end
position of a given range under test.
Like cursor-info, range info (""source.request.cursorinfo"") answers some
questions clients have for a code snippet under selection, for instance, the type of a selected
expression. This commit implements this new quest kind and provides two
simple information about the selected code: (1) the kind of the
snippet, currently limited to single-statement and expression; and (2)
the type of the selected expression. Gradually, we will enrich the
response to provide more insight into the selected code snippet.