[kutil] Add kutil::map hash map

Added the kutil::map collection, an open addressing, robinhood hash map
with backwards shift deletes. Also added hash.h with templated
implementations of the FNV-1a 64 bit hash function, and pulled the log2
function out of the heap_allocator code into the new util.h.

modules.yaml

@@ -318,6 +318,7 @@ modules:
             - src/tests/logger.cpp
             - src/tests/heap_allocator.cpp
             - src/tests/main.cpp
+            - src/tests/map.cpp
             - src/tests/vector.cpp
 overlays:
     - url: https://f000.backblazeb2.com/file/jsix-os/sysroot-llvm8-20190706.tar.bz2