fix various typos

Changelog

doc/codecs.texi

doc/encoders.texi

doc/examples/decoding_encoding.c

doc/faq.texi

doc/muxers.texi

ffmpeg.c

libavcodec/aacdec.c

libavcodec/avcodec.h

libavcodec/dcadec.c

libavcodec/dcaenc.c

libavcodec/diracdec.c

libavcodec/indeo5.c

libavcodec/jpeg2000.c

libavdevice/opengl_enc.c

libavfilter/buffersrc.h

libavfilter/libmpcodecs/vf.h

libavfilter/libmpcodecs/vf_fspp.c

libavfilter/vf_mp.c

libavfilter/vf_smartblur.c