Add note about JRuby not working

Concerns #254
Move the badges to the top

[ci skip]
Add a 4.0.0.rc disclaimer in the readme
Caching of raw info values.
Fixed #+ method so it only affects the last argument
Merge pull request #259 from nandinga/raw-info-caching

Caching of raw info values.
Merge pull request #258 from nandinga/fix-plus-modifier

Fixed #+ method so it only affects the last argument
Add ability to silence errors more elegantly

Fixes #257
Refactor MiniMagick::Tool::OptionMethods
Remove JRuby and MRI 1.9.2 from Travis

* We remove JRuby because the "open3" library doesn't work on it.
* We remove MRI 1.9.2 because it's already end of life.
Added support for multi-parameter options
Merge pull request #260 from nandinga/multi-parameter-options

Added support for multi-parameter options
Output any eventual stderr from commands

The `compare` command-line tool operates in the sense that it outputs
it's info to stderr, which is very strange, but we would like to support
that. This way, people could do:

  compare = MiniMagick::Tool::Compare.new(false)

  # Do something with compare ...

  $stderr = StringIO.new
  compare.run
  output = $stderr.string
  $stderr = STDERR

It's not really pretty, but I think this is the best we can do, since
using stderr should be ultimatively fixed in ImageMagick.

Fixes #257
Correct typo
Merge pull request #265 from slant/patch-1

Correct typo
Update README.md

Small correction on the code.
Merge pull request #266 from basex/patch-1

Update README.md
Show the optional usage of combine_options in ::new

This feature was added for 4.0.0, but is not documented. Now it is!
Add respond_to_missing? to complement method_missing

The `#respond_to_missing?` hook is the complement of `#method_missing`,
used by `#respond_to?`, `#method`, etc... to do the right thing. In this
case, since `#method_missing` is implemented in terms of an instance of
`MiniMagick::Tool::Mogrify`, we use an instance of that class to
determine if objects of this class can respond to those missing
messages.
Merge pull request #269 from stevenharman/add_responds_to_missing_to_image

Add respond_to_missing? to complement method_missing