`--human_readable` option

[dylanpilz]

Add a flag to display output in "human readable" format, consistent with original freyja implementation, where translations are displayed next to nt mutations. This makes parsing harder for downstream tasks but can be useful for debugging.

For example:

nt_mutations,aa_mutations
C21618T T21632-TACCCCCTG,S:T19I S:DEL25/27

becomes

mutations
C21618T(S:T19I) (T21632-TACCCCCTG)(S:DEL25/27)