Refactor Config

[kyrylo]

Fixes #1843 (Rework the Pry config)

There are a few breaking changes. They are mostly minor, so I decided not to
indroduce deprecations because it will considerable slow things down.

Key changes:

• Pry.lazy was replaced with Pry::Configuration::LazyValue

  The config accepts three values now LazyValue, MemoizedValue and simply
  Value. The main difference is that:

  • Value is any value, including procs (so that an option returns a raw
    proc)
  • LazyValue is a proc that is call on every invocation of an option
  • MemoizedValue is a value that is called only once (and then the option
    always returns the return value of the )

• Pry.config.history was a meta-option that held suboptions. However, the new
  config doesn't permit that (unless you know what you do)

  Instead, we introduce a few options. For example:

  • Pry.config.history.histignore becomes Pry.config.history_ignorelist
  • Pry.config.history.file becomes Pry.config.history_file
  • and so on

  This was done so we can simplify configuration merging. Inlining option makes
  configuration implementation simpler, without losing much. The rule is that
  you want to keep your options under your prefix (if you are a
  plugin). Therefore, say, Pry.config.pry_rescue.* should be
  Pry.config.pry_rescue_* if you need merging.

The rest should behave in a similar fashion (and I rely heavily on our test
suite to claim so).