Increase MaxValueSize for a reasonable value

10MB for a blob is a really tiny size, I'd like to decide myself the size of values I'm going to push. And it seems to me that all blobs smaller than 1GB shouldn't be harmful for the ledis, so just lift up this limit please.
add SETEX command for KV
Merge pull request #99 from holys/develop

add SETEX command support for the KV data structure
update config
update bench tool
update protocol handling
update benchmark
add slice for store, optimize leveldb/rocksdb get
set replication config to false default
add reap protocol benchmark
rename to dbbench using ledis
refactor db getslice
add go slice
optimize benchmark

thanks joe
optimize and bugfix TTL, must upgrade manually
add flag upgrade-ttl
update benchmark
bugfix ledis-dbbench
add GetSlice, hope can improve get performance
update config