Corrected names of namespace environments

environmentName() should return the package name without
the "namespace:" prefix.
Rationalized Read/Write context

Moved contexts for RDataReader and RDataWriter to
top level. Makes it easier to use these classes for
independent serialization/deserialization of R data
objects
Bumped up to newer version of maven-assembly-plugin

Older version was forking the build to construct
the jar and zip archives
Corrected indentation in package poms
Add support for string arguments to library()
Implemented Date2POSIXlt, POSIXlt2Date

Also corrected conversion from double to string-
turned off digit grouping that was creating problems
everywhere
Added tests for environment name formatting
Merge branch 'master' of github.com:bedatadriven/renjin