Possible memory optimizations

[cmdcolin]

Some amount of optimization could be done to keep memory usage lower

For example: the each read has a seq field (and others) that are decoded to a string. But strings are 16 bits per letter, because js is utf16

Therefore, a potential memory optimization would be to either (a) use a Uint8Array instead or even (b) decode the 4bit raw encoding from BAM backing buffer on demand

probably (a) would be interesting to try as a first step and see what impact it has on loading larger files with e.g. deep coverage

similar issue in cram-js GMOD/cram-js#135