Switch resource.meta to be an object.

[danielgtaylor]

This changes the behavior of the meta object in a backward-incompatible
way. It goes from being a dict to an instance of a ResourceMeta class.
Example:

import boto3

s3 = boto3.resource('s3')

# The old way
s3.meta['service_name']
s3.meta['client']

# The new way
s3.meta.service_name
s3.meta.client

cc @jamesls, @kyleknap

[coveralls]

Coverage increased (+0.02%) when pulling 9f3f4ec on meta-object into bc866bb on develop.

[jamesls]

I think stylistically we should always be using "is not None" if we are comparing against None, which in this scenario we are.

[jamesls]

Looks good, just some small questions on the ResourceMeta class itself.

[coveralls]

Coverage decreased (-0.1%) when pulling c48ecc8 on meta-object into bc866bb on develop.

[jamesls]

[coveralls]

Coverage increased (+0.04%) when pulling e31eba1 on meta-object into bc866bb on develop.