Explicit strand usage across codebase

[mbhall88]

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Off the back of #238 and #239 I think this is a fairly high priority.

Right now we have some worringly discrepant ways of dealing with strand within the codebase.

For example

https://github.com/rmcolq/pandora/blob/0f1210e6927b905c0a1fe03612ed067d73471851/include/minihit.h#L23

where we have a boolean representing read_strand. It is not at all obvious what true maps to from reading this. My intuition was that true would refer to forward strand, but I think it is actually the opposite. Anyway, the point is this should be completely unambiguous by using the new pandora::Strand enum class introduced in #239

[leoisl]

I agree, and your solution is a proper one!