enabling cpp-netlib to be compiled into a sincle library

this adds the CMake variable 'CPP-NETLIB_BUILD_SINGLE_LIB', which
defaults to OFF and will enable build of a single library 'libcppnetlib'
to be compiled instead of the different separated libraries.

the tests and examples have been adjusted to deal with a single library

the uri submodule has also been changed
include uri-changes related to previous commit
fix duplicate target definition in uri
Merge pull request #227 from torbjoernk/make-one-lib

Enable cpp-netlib to be build into a single library