Example programs for TCP and UNIX Sockets clients

Both examples are provided in Haddock documentation and also as
standalone files. Haddock documentation also describes how that examples
may be tested and what the test results actually mean.
Haddock for create{Tcp,Unix}ClientPool and with{Tcp,Unix}ClientConnection

Trying not to duplicate too much documentation from resource-pool
package. It could get out of date fairly quickly.