Primary change is to cleanup code and remove duplicated code.
1. Unify the rc file reading into libdispatch/drc.c. Eventually extend
if we need rc file for netcdf itself as opposed to the dap code.
2. Unify the extraction from the rc file of DAP authorization info.
3. Misc. other small unifications: make temp file, read file.
4. Avoid use of libcurl when reading file:// because
there is some kind of problem with the Visual Studio version.
Might be related to the winpath problem.
In any case, do direct read instead.
5. Add new error code NC_ERCFILE for errors in reading RC file.
6. Complete documentation cleanup as indicated in this comment
https://github.com/Unidata/netcdf-c/pull/472#issuecomment-325926426
7. Convert some occurrences of #ifdef _WIN32 to #ifdef _MSC_VER
