av: Rename lex to h264 or h264lex

[Alan Noble]

In future we will need support for H.265 and will need to differentiate the H.265 lexer from the H.264 lexer.

[kortschak]

It's not clear to me what this is wanting. We have ".../av/stream/lex" which has both H264 and MJPEG. We also have revid.Revid.lexTo which has a signature that matches both of those. Can't we just add H265 to "lex"?

[Alan Noble]

Ah, yes, quite right.

[Alan Noble]

Add H265 under existing lex instead.