Note this differs from the other trees in the package in inclusion of "contig" parameter,
because underlying cgranges has built-in hashmap and essentially stores multiple trees.
Passing a \0-terminated C string contig will be faster than passing a D string or char[],
due to the need to call toStringz before calling the C API.
last param "label" of cr_add not used by cgranges as of 2019-05-04
Insert interval for contig
Note this differs from the other trees in the package in inclusion of "contig" parameter, because underlying cgranges has built-in hashmap and essentially stores multiple trees. Passing a \0-terminated C string contig will be faster than passing a D string or char[], due to the need to call toStringz before calling the C API.
last param "label" of cr_add not used by cgranges as of 2019-05-04