use xpall easy for debug

use xpall to show more debug message
Merge pull request #187 from niuys/master

'queue' use xpall easy for debug
ready for v0.8.0
Merge pull request #188 from cloudwu/dev

release v0.8.0
fix issue #189
free buffer
fix issue #190
harbor can post error message back when the destination is not exist
Merge branch 'master' of github.com:czlc/skynet-1 into czlc-master
Merge branch 'czlc-master' into dev
skynet_free(NULL) is ok
merge lua bugfix, read http://www.lua.org/bugs.html