Renames --vectors-only to --opt-cell-lengths to reduce confusion that this is in addition to optimizing cell positions.
Renames --fully-opt to --opt-cell-fully for consistency (if we ever add something like --opt-cell-angles, this would be equivalent to both being true, which feels reasonably consistent)
Resolves #180
--vectors-onlyto--opt-cell-lengthsto reduce confusion that this is in addition to optimizing cell positions.--fully-optto--opt-cell-fullyfor consistency (if we ever add something like--opt-cell-angles, this would be equivalent to both being true, which feels reasonably consistent)Still open to further suggestions