This is mostly involved with moving CMAKE_SOURCE_DIR and
CMAKE_BINARY_DIR to PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR because it
enables zeek to be built as a subproject of another.
There is another branch in the cmake repository with the same name that
is also required for this to fully work.
For backward compatibility when reading values, we first check
the ZEEK-prefixed value, and if not set, then check the corresponding
BRO-prefixed value.
This also installs symlinks from "zeek" and "bro-config" to a wrapper
script that prints a deprecation warning.
The btests pass, but this is still WIP. broctl renaming is still
missing.
#239
