Infer type in bamfile

[dotinspace]

There is an issue with libc on aarch64, in that it has c_char aliased to u8, whereas on amd64 libc uses i8 for c_char. The result of this is that pyd4 does not build correctly in docker containers on aarch64, verified on both Apple M1s and RPi4.

A solution to this appears be to let the compiler infer types in bamfile.rs L102, instead of specifying i8/u8.

[ggozad]

This works on my M1 and appears to close #58