0.1.2 alpha release

Various fixes and minor interface changes.

• fixed redis-rb dependency to >= 3.3.2 and < 4 for now
• added basic roadmap to Readme
• fixed issue in Redstruct::Connection where blocks were not being passed on to proxied method
• fixed issue in Redstruct::Connection where pipelining commands would not reuse the same connection (note: still, avoid pipelining for now and use Lua scripts)
• fixed Redstruct::Set#pop and Redstruct::Set#random to have similar interface to Redstruct::List#pop (i.e. popping one element returns it, popping more returns a set)
• added support for pexpire and pexpire_at, plus better documentation in Redstruct::Struct
• Minor linting