Support validation of draft-04/hyper-schema

(Tests are part of the JSON-Schema-Test-Suite submodule; my PR hasn't been
merged upstream yet, though)

Given that I didn't actually need to change anything important to get the
validator to validate test schemas, I'm not entirely convinced that I've
done the right thing here -- or else the architecture of the validators is a
bit overengineered.
Make intra-doc refs work when validating with :fragment

Here's a weird corner-case for you: when calling JSON::Validator.validate
and using the :fragment option, any references to other parts of the same
schema would fail.  Why?  Because the handling of :fragment involved
creating a *new* schema, with a new URI, with a subset of the original
schema.  Internal refs (as handled by JSON::Schema::RefAttribute) would try
to resolve the ref within this sub-schema, and go *fwackoom* because the
structure of the sub-schema wouldn't have the right path in it.

I've adjusted the code for schema_from_fragment to not call
initialize_schema (and hence not create those new sub-schemas), and instead
just create a new JSON::Schema object (which, according to the comments, is
the only reason that initialize_schema was being called).  This causes no
new schemas to be created, and RefAttribute can go looking up its ref in the
right place.
Added codeclimate badge to readme
Use IPAddr class to validate ip formats
And another 1.9.3 compatibility fix
Stopped parsing dates using regular expressions, and instead used Ruby's
own iso8601 parsing method

The initial reason for this was that date-time should allow 'YYYY-MM-DD'
according to iso8601. Ruby allows this but schema-form did not.
Stopped all formats requiring uri

I assume that's a hangover from when they were all in the same file as
the uri format
Add description for custom format usage
Update format list
Improve description
Also test schema dependencies in draft-04
Add byebug as development dependency
Remove byebug again
Merge pull request #144 from RST-J/update_descr

Update descr
Merge pull request #141 from iainbeeston/codeclimate

Added codeclimate badge to readme
Merge pull request #143 from RST-J/fix_ip_formats

Use IPAddr class to validate ip formats
Merge pull request #145 from RST-J/fix_schema_dep_v4

Fix schema dep v4
Merge pull request #127 from mpalmer/fragment-validation-with-ref

Make intra-doc refs work when validating with :fragment
Merge pull request #118 from iainbeeston/ruby_validation_of_dates

Conflicts:
	lib/json-schema/attributes/formats/ip4.rb
	lib/json-schema/attributes/formats/ip6.rb
Merge pull request #125 from mpalmer/hyper-validation

Hyper validation