show-source: Indicate all monkeypatches can be shown with -a

Fixes #849
ShowDocSpec: fix indentation

"The snake which cannot cast its skin has to die.
As well the minds which are prevented from changing
their opinions; they cease to be mind."

  - Friedrich Nietzsche
Config: wrap everything at 80 characters

Conflicts:
	lib/pry/config.rb
PryClass: get rid of obsolete comment

The "ls" command uses tabular output by default (where possible).
Rubygem: fix raising of CommandError for #install

Fix issue #870 (gem-install seems broken on jruby)
Hist: fix `--exclude-pry` switch

Fix issue #874 (hist -e breaks with TypeError: can't convert
Pry::Code::LOC to String)

And add a test for that switch.
CLI: link to pryrepl.org instead of github

And apply a couple of cosmetic fixes.
CLI: output help when unknown switches are used

Fix issue #847 (Pry should output help when unknown flags are used)