[sane-devel] Found a few minor typos in backend-writing.txt

[jazz_johnson at verizon.net]

$ diff backend-writing.txt.original backend-writing.txt
125c125
<     directories. This is especially usefukl for frimware directories. See
---
>     directories. This is especially useful for firmware directories. See
129c129
<     complexity of the backend, splitting it toseveral files can be 
appropriate,
---
>     complexity of the backend, splitting it to several files can be 
appropriate,
224c224
<   not use miltiple libraries e.g. for lower and higher level code.
---
>   not use multiple libraries e.g. for lower and higher level code.