add hexstr_to_bytestring bif that does exactly the opposite of
bytestring_to_hexstr.
Merge remote-tracking branch 'origin/topic/bernhard/hexstr'

BIT-1069 #merged

* origin/topic/bernhard/hexstr:
  add hexstr_to_bytestring bif that does exactly the opposite of bytestring_to_hexstr.
Updating submodule(s).

 [nomail]
Updating submodule(s).

 [nomail]