contest: support_lzo? always return false

Because Groonga >= 4.0.7 does not support LZO compression.
context test: follow LZO compression support change
context: add Groonga::Context#support_lz4? method
context test: add Groonga::Context#support_lz4? test
extconf: require Groonga 4.0.7
context: translate comments
context: fix comment style
extconf: add get processor number method

It may build speed up. :)
extconf: use 2 or more processors for building if avaliable

Travis CI terminates CI job when no output has been recived in the last 10 minutes. :<