+ past $length. Grows $to if necessary. Doesn't need to allocate any extra
+ memory.
+
+ "vshift $v, $start, $length => $bits [, $insert ]"
+ In the area starting at $start and of length $length in $v, shift bits
+ "abs $bits" positions left if "$bits > 0" and right otherwise. If
+ $insert is defined, also fills the resulting gap with ones if $insert is
+ true and zeros if it's false. Bits outside of the specified area are
+ left untouched. Doesn't need to allocate any extra memory.
+
+ "vrot $v, $start, $length, $bits"
+ In the area starting at $start and of length $length in $v, rotates bits
+ "abs $bits" positions left if "$bits > 0" and right otherwise. Bits
+ outside of the specified area are left untouched. Currently allocates an
+ extra buffer of size "O($bits)".