fix: match reader to the number of bytes in elements
fix: when vm is wrong, retreturn appropriate number of elements
fix: return singleton when num_elem is one
BF+ENH: Improve value extraction.

Fixes a issue with unpacking values with implicit VR and a VM > 1.
Allows incorrect VM with implicit VR, just issues a warning.
Allows conversions to be applied to unpacked values.
Merge pull request #1 from moloney/pr-17-update

BF+ENH: Improve value extraction.
Merge pull request #17 from satra/fix/VM

fix: match reader to the number of bytes in elements