fix Pry.view_clip().

before:
[3] pry(main)> Pry.view_clip(_pry_)
=> "#<Pry>"

after:
[19] pry(main)> Pry.view_clip(_pry_)
=> "#<Pry:7f97e16d7bc8>"
forgot hex prefix
change Pry.view_clip() to optionally drop or include hex value.

change 2nd argument of Pry.view_clip() to accept a Hash of options
with two keys: max_length (default 60) and id (default false)

the custom prompt proc's in lib/pry.rb clip the object shown to
look better visually. this change still supports that behavior but
also adds the option to include a hex representation of the object's
ID by including id: true.

@rf- suggested supporting both (with & without id) to be able to
keep printer proc's pretty but also support other code that's okay
with printing inspects that are hex-y, like the Pry::CLIPPED_PRINT.

also changes Pry::CLIPPED_PRINT to print return values with a hex
ID included since it is a bit different from prompt proc's.
improve err msg & method name.
Merge pull request #1162 from pry/viewclip-options

change Pry.view_clip() to optionally drop or include hex value.