spelling/wording

Originally committed as revision 7859 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/avutil.txt

 AVUtil
 ======
-libavutil is a small lightweight library of generally usefull functions
-it is not a library of code which is needed by both libavcodec and libavformat
+libavutil is a small lightweight library of generally useful functions.
+It is not a library for code needed by both libavcodec and libavformat.
 
 
 Overview:
@@ -12,26 +12,26 @@ fifo.c                  resizeable first in first out buffer
 intfloat_readwrite.c    portable reading and writing of floating point values
 log.c                   "printf" with context and level
 md5.c                   MD5 Message-Digest Algorithm
-rational.c              code to perform exact calculation with rational numbers
+rational.c              code to perform exact calculations with rational numbers
 tree.c                  generic AVL tree
 crc.c                   generic CRC checksumming code
 integer.c               128bit integer math
 lls.c
 mathematics.c           greatest common divisor, integer sqrt, integer log2, ...
-mem.c                   memory allocation routines with guranteed alignment
+mem.c                   memory allocation routines with guaranteed alignment
 softfloat.c
 
 Headers:
-bswap.h                 big/little/native endian conversation code
-x86_cpu.h               a few usefull macros for unifying x86-64 and x86-32 code
+bswap.h                 big/little/native-endian conversion code
+x86_cpu.h               a few useful macros for unifying x86-64 and x86-32 code
 avutil.h
 common.h
-intreadwrite.h          reading and writing of unaligned big, little and native endian integers
+intreadwrite.h          reading and writing of unaligned big/little/native-endian integers
 
 
 Goals:
 ======
 * Modular (few interdependancies and the possibility of disabling individual parts during ./configure)
 * Small (source and object)
-* Efficient (low cpu and memory usage)
-* Usefull (avoid useless features almost noone needs)
+* Efficient (low CPU and memory usage)
+* Useful (avoid useless features almost noone needs)