Release 1.6: hfile_libcurl improvements; more checks on input files * Fixed bug where iterators on CRAM files did not propagate error return values to the caller correctly. Thanks go to Chris Saunders. * Overhauled Windows builds. Building with msys2/mingw64 now works correctly and passes all tests. * More improvements to logging output (thanks again to Anders Kaplan). * Return codes from sam_read1() when reading cram have been made consistent with those returned when reading sam/bam. Thanks to Chris Saunders (#575). * BGZF CRC32 checksums are now always verified. * It's now possible to set nthreads = 1 for cram files. * hfile_libcurl has been modified to make it thread-safe. It's also better at handling web servers that do not honour byte range requests when attempting to seek - it now sets errno to ESPIPE and keeps the existing connection open so callers can revert to streaming mode it they want to. * hfile_s3 now recalculates access tokens if they have become stale. This fixes a reported problem where authentication failed after a file had been in use for more than 15 minutes. * Fixed bug where remote index fetches would fail to notice errors when writing files. * bam_read1() now checks that the query sequence length derived from the CIGAR alignment matches the sequence length in the BAM record.