Revert "Revert "Enable the ignore_unknown_field option in the Ruby unmarshal options" (#5511)" (#5533)

* Revert "Revert "Enable the ignore_unknown_field option in the Ruby unmarshal options" (#5511)"

This reverts commit be1716a6.

* Separate ruby conformance test on Mac

* Fix shell syntax

* Fix test

This adds the ability for the MRI Ruby library to optionally pass in a
ignore_unknown_fields option when decoding JSON. The functionality was
added upstream in upb, this change exposes that option.

* This allows for ruby code to catch and handle Protobuf
    TypeErrors separately from the standard Ruby TypeError

  * Maintains backwards compatibility by having the new
    Google::Protobuf::TypeError inherit from the base
    TypeError. Any code that was catching TypeError should
    continue to work.

This will allow loading the extension for Ruby 2.1.10...

Change-Id: If7b1cc0f03f609a7f43ddafc8509b44207c60910

This involved fixing a few important bugs in the
Ruby implementation -- mostly cases of mixing
upb field types and descriptor types (upb field
types do not distinguish between int/sint/fixed/sfixed
like descriptor types do).

Also added protobuf-specific exceptions so parse
errors can be caught specifically.

Change-Id: Ib49d3db976900b2c6f3455c8b88af52cfb86e036

* make consistent between mri and jruby
* create a #to_h and have it use symbols for keys
* add #to_json and #to_proto helpers on the Google::Protobuf message classes

starting to make `RepeatedField` quack like an array

additional changes:
* make sure gemspec gets all ruby code files
* add homepage in gem spec removes one of the warnings, and the gem spec authors are pushing
everyone to include a homepage in the gem
* remove excess whitespace in test suite to bring formatting inline with the rest of the file

system. The Ruby module build now uses an amalgamated distribution of
upb, and successfully builds a Ruby gem called 'google-protobuf' with
module 'google/protobuf'.

This adds a Ruby extension in ruby/ that is based on the 'upb' library
(now included as a submodule), and adds support for Ruby code generation
to the protoc compiler.

  General
  * License changed from Apache 2.0 to New BSD.
  * It is now possible to define custom "options", which are basically
    annotations which may be placed on definitions in a .proto file.
    For example, you might define a field option called "foo" like so:
      import "google/protobuf/descriptor.proto"
      extend google.protobuf.FieldOptions {
        optional string foo = 12345;
      }
    Then you annotate a field using the "foo" option:
      message MyMessage {
        optional int32 some_field = 1 [(foo) = "bar"]
      }
    The value of this option is then visible via the message's
    Descriptor:
      const FieldDescriptor* field =
        MyMessage::descriptor()->FindFieldByName("some_field");
      assert(field->options().GetExtension(foo) == "bar");
    This feature has been implemented and tested in C++ and Java.
    Other languages may or may not need to do extra work to support
    custom options, depending on how they construct descriptors.

  C++
  * Fixed some GCC warnings that only occur when using -pedantic.
  * Improved static initialization code, making ordering more
    predictable among other things.
  * TextFormat will no longer accept messages which contain multiple
    instances of a singular field.  Previously, the latter instance
    would overwrite the former.
  * Now works on systems that don't have hash_map.

  Python
  * Strings now use the "unicode" type rather than the "str" type.
    String fields may still be assigned ASCII "str" values; they will
    automatically be converted.
  * Adding a property to an object representing a repeated field now
    raises an exception.  For example:
      # No longer works (and never should have).
      message.some_repeated_field.foo = 1

committer: Jon Skeet <skeet@pobox.com>