Missing minBlockLength and maxBlockLength in ttl

[hmollercl]

Hi, according to lv2 when using fixedBlockLength, minBlockLength and maxBlockLength must be provided.
https://lv2plug.in/ns/ext/buf-size#fixedBlockLength

since buffer

"These effects are supposed to work well with the following values of Frames/Period: 64, 128, 256, 512"

my sugestion is to put in the ttl:

lv2:requiredFeature bsize:fixedBlockLength, bsize:powerOf2BlockLength,
       bsize:boundedBlockLength ;
bsize:minBlockLength 64 ;
bsize:maxBlockLength 8192 ;

There are hosts that use buffer assembly according to this values.

[hmollercl]

created this pull request to fix this issue #18