Reformatting this to 80-columns and wordsmithed slightly

Is one of my windows no longer 80-columns?  How did those creep in...!?!
Update descriptions of GMP/RE2 to match new behavior
Oops -- fixing setchplenv.* script names

I called these scripts the wrong thing in my previous commit.  Noticed
some other places where they were referred to and should be referred
to and updated those as well.
Fixing a grammatical issue (and more wordsmithing)
Adding a trailing slash
Adding reminders that the unset behavior was described in the preceding par.

(for those with ultra-short memories)
Merge pull request #521 from bradcray/README-edits-1.10

Edits to README.chplenv and util/README

* the new GMP/RE2 behavior
* the new setchplenv.* scripts (particularly the quickstart versions)

Fixed some 80-column issues that I injected the other day in util/README