Specify rake and rspec versions in gemspec

Since the development dependency versions are undefined, gem just grabs
the latest of everything. But the specs are failing under RSpec 3.0.0.
Specify Rubinius version

The build is currently failing because no binary package is available
for 'rbx'. According to The Internet, specifying the version might help.
And that seems like a good idea, anyway.
loosen dependency on redis-rb to allow v3.1.x

Resolves #84
Resolves #85
add specs for zinterstore
brpop: properly de-namespace retrieved key; resolves #78
Add support for the future deprecation of unknown command handling.
1.4.1 -> 1.5.0 changelog [ci skip]
Add support for REDIS_NAMESPACED_DEPRECATIONS env variable
add missing specs for pending example groups with implementations
borrow test helpers verbatim from redis-rb, use try_encoding
Add encoding comment to ensure string literals are handled correctly
Add hyperloglog commands
Merge branch 'adammck/add_hyperloglog_commands'

Resolves #82
target hyperloglog specs against >= 2.8.9
cleanup: kill some deprecation warnings in specs
Update changelog for hyperloglog [ci skip]
Extract shared example

This is to be able to run the specs on different namespaces
Adds the ability to pass a Proc as namespace
Add examples for changing namespace with Proc
Add some tests for Redis::Namespace#namespace