Remove necessity to manually specify LCB library versions

This is probably not going to be an issue again for some time, but at present we manually specify the libcouchbase DLL names in our build file, when they could theoretically be automatically inferred, either by scanning the LCB build directory, or by using the CMake file here:

https://github.com/couchbase/libcouchbase/commit/69f9a4eb8414f4bfd3824b863701d89a313401d5

The latter approach could involve parsing the CMake file (probably somewhat fragile although there are some attempts at a Python API for this in PyPI), or by fixing the issues with a full CMake build (only seen on Mac so far). The latter approach seems most desirable as it leads to a fully accurate rendering of the build in CMake-capable editors/IDEs. I guess one approach would be to use full CMake build for anything except Mac where the filenames seem not to change, although this is less consistent than would be desirable.