Add some information about why libpnet is useful to the README.
Implement FromStr for MacAddr.
Fix incorrect buffer sizes with bpf

When using BPF, the read buffer was being initialised to the size of the write
buffer, rather than read buffer.
Remove an unnecessary copy when sending packets using datalink_channel().

NOTE: The copy still exists on Windows - since Windows support is currently
broken anyway.
Add some data link benchmarks.

Note that the C version only works on OS X.
Update for rust rfc 52 changes
Update lipnet api to conform to rfc 52
Fix build with latest Rust nightlies.
Merge pull request #6 from ebfe/rfc-52

Update for rust rfc 52 changes
Fix Windows build.