minor tweaks to web documentation

minor tweaks to web documentation

* doc/ref/web.texi: Say `World Wide Web'; the hyphenated form is almost
  never used (c.f. w3.org).

  General predicate arguments are named `obj'.  Fill in arguments
  omitted from some procedure definitions (e.g. `request-method').

  Minor tweaks, such as using en-dash and missing markup as appropriate.
  Wrap very long deffn lines.

* module/web/*.scm: Expand texinfo markup in doc strings.  Synchronize
  with changes in web.texi.