Consistently use FetchContent and PkgConfig for handling dependencies (#74)

* Handle the PCRE dependency with FetchContent
If the system has regcomp(3) do not link against the pcreposix library,
unless CBF_WITH_PCRE is set; that is not what CMakeLists.txt used to do.
Build either shared or static cbf, fcb, and img libraries, but not both;
that is what PCRE does.

* Handle the HDF5 dependency with FetchContent
Make the h5dump.cmake script config-aware.  Nothing uses zlib anymore.

* Handle the CQRlib dependency with FetchContent
No more ExternalProject.

* Reorder LibTIFF for consistency with other FetchContent-handled dependencies

* Cleanup
* Default to BUILD_SHARED_LIBS ON
* Do not overlink the fcb and img libraries against HDF5
* cbf_hdf5 does not need pcreposix.h or regex.h

Author: hattne