Improve remote helper documentation

These patches have already been sent on the mailing list. They've been discussed extensively, and have been through several revisions. The first three patches are already in pu, but are stalled because they haven't been ack'ed. The purpose of this resend is get everything neatly organized so they can be ack'ed by remote helper experts and merged into master.

Everything is based on the topic branch rr/remote-helper-doc.

Ramkumar Ramachandra (5):
Documentation/remote-helpers: Rewrite description Documentation/urls: Rewrite to accomodate <transport>::<address> Documentation/remote-helpers: Add invocation section
Fixup: Second argument may be any arbitrary string Documentation/remote-helpers: Fix typos and improve language

 Documentation/git-remote-helpers.txt |  117 ++++++++++++++++++++++++----------
 Documentation/urls.txt               |   58 ++++++++++-------
 2 files changed, 115 insertions(+), 60 deletions(-)