I added the branch 'prefix' in my cowstrings library. For a simple sorting
[benchmark](https://github.com/planetis-m/cowstrings/blob/prefix/tests/bcowstrings3.nim)
I get 0.1704 ms (prefix String) vs 0.1944 ms (std.string) average time for
sorting a seq of a thousand objects. For now I don't have a solution for
l-value modifier since there's no way to update prefix.
proc `[]`*(x: var String; i: int): var char {.inline.} =
checkBounds(i, x.len)
result = x.p.data[i]
# if i < 4:
# x.prefix[i] = val??
Run
