Improve validity checks when loading BIOM file

[sfiligoi]

When loading a BIOM file, we do not always check that our assumptions are correct.

An example is
load_indptr
where we blindly assume that all elements are uint32_t.

unifrac-binaries/src/biom.cpp

Line 153 in f5fd2a5

uint32_t *dataout = (uint32_t*)malloc(sizeof(uint32_t) * dims[0]);

This may result in a memory corruption if the file is malformed, and the type is not correct.

Note that we already have some limited error handling, but we should extend it.