cppsp: make websocket support optional

run ./configure --disable-websocket (in the package_cppsp output dir) to
disable websocket support
cpoll: improved error handling
cppsp: proper error handling when finding a module by name fails
cppsp: minor fixes in package_cppsp
cppsp: load modules in the order that they are specified
cppsp: exit parent process when all children have exited
cppsp: minor bugfixes

* properly handle 0-length responses
* close connection immediately when write errors occur
package_cppsp: makefile: properly link libcppsp.so

libcppsp uses functions in libcpoll, so it should be linked to libcpoll
cppsp: added some documentation
misc