add hashCode and equals to Module.

This ensures that a set which collects modules only contains one
instance of the GuavaModule.
add support for serializing and deserializing Guava Ranges
Bump guava version to 15.0 (released 2013-09-06)
Merge pull request #35 from youdevise/guava-15-upgrade

Bump guava version to 15.0 (released 2013-09-06)
Merge pull request #32 from hgschmie/master

add hashCode and equals to Module.
Merge pull request #34 from cponomaryov/master

Use Optional type parameter if present to create JSON schema
Merge pull request #33 from ispringer/feature-range

add support for serializing and deserializing Guava Ranges
...
Improved handling of Range, to work with polymorphic types.
...
prepare for 2.3.1
[maven-release-plugin] prepare release jackson-datatype-guava-2.3.1
[maven-release-plugin] prepare for next development iteration
add support for Guava 10 through 13 to the Range deserializer; Guava 10-13 required using the com.google.common.collect.Ranges utility class, which was removed in Guava 14, to instantiate Ranges
Merge pull request #36 from ispringer/feature-range-fix

add support for Guava 10 through 13 to the Range deserializer
update release notes wrt #36