Take a stab at implementing a simpler clone

Literally clone the subrepo into subdir (at branch) and add the .gitrepo
file. Does it need to be more complicated than this?
Make a better commit msg

* short msg is subrepo command
* long msg is all info in pretty json

meta field 'former' is now 'parent' (the HEAD before a clone or pull)
this value is not self referential, so can aid in fewer commits
notes and links
rename a variable
get rid of duplicate var
Add remote and upstream branch on fetch.

Will add a config option to stop this, but 'gsr clean' already cleans up.

Now the subrepo remote is always available.
Changing former to parent broke this:
notes
Use more plumbing in clone:

The prior clone command used too much porcelain stuff.
Fix missing line continuation
update todo