Merge pull request #71 from omeid/master

Typed Errors. Closes #69
identify error kind by using an error code int; test the error codes
thanks to Omeid; and a minor correction in code comment
fix a bug in query intersection and complement
mark 3.1.1
Correct Map for file sizes larger than 1<<31 - 1

int(int64value) doesn't always return <0 when an int is 32 bits.
Long ago, Go moved to 64 bit int's on amd64 and mmap-ing large files works fine.
Should not panic when an error return is the sane thing to do.
Remove un-used ANON (which should probably have been set to syscall.MAP_ANON anyway).
Merge pull request #73 from dchapes/patch-1

Correct Map for file sizes larger than 1<<31 - 1
sync with doc
Merge pull request #1 from HouzuoGuo/master

Update with upstream.