fix running http-client_test with 'make test'

when issuing 'make test' the http-client_test were not found due to
wrong parameter in add_test() call
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 build of shared libraries

even if CPP-NETLIB_BUILD_SHARED_LIBS was set to ON or TRUE, the shared
libraries were not build unless BUILD_SHARED_LIBS also was enabled.

now either of the two needs to be set to enable shared libraries.
fix duplicate target definition in uri
Merge pull request #226 from torbjoernk/fix-client-test

cpp-netlib-http-client_test fails when triggered through `make test`
Merge pull request #228 from torbjoernk/fix-shared-libs

fix build of shared libraries
Merge pull request #227 from torbjoernk/make-one-lib

Enable cpp-netlib to be build into a single library