Merge branch 'barry/update-sowing'

Conflicts:
tutorials/HandsOnExercise.html

Move install.py and gmakegen.py from lib/petsc-conf/ to config/

update to use Sowing 1.17
fixed many documentation errors as well

unstall now deletes petsc specific directories created by PETSc
also don't use exists() so that softlinks to libraries are also deleted

do not copy over install.py gmakegen.py or sowing to --prefix location

did not include proper quotes for files to exclude in installation due to line feed
cannot fix in git history because git is silly and doesn't like fixes of things that have been pushed

with --prefix installs don't copy over any downloaded sowing or text processing tools used only by PETSc

manual merge of conflict