uSTL config.h clash

Hi Uwe

There's a problem with uSTL's config.h clashing with a header file used
by the SNMP library package. In this case, it is clear that the uSTL
header files should not be polluting the top-level include/ directory
unless this is necessary as part of the contract with application code.

I note that the upstream version of "ustl.h" looks for the other headers
in a ustl/ subdirectory. Are you able to move all the other headers
(including config.h) into include/ustl/ within the package without
disrupting the rest of the sources too much?

John Dallaway