Polish the systick a little
Modify the K20 example to check the systick flag
[fix] warning: use of deprecated item: prefer using indexing
Merge pull request #112 from errordeveloper/use_index_instead_of_get

[fix] warning: use of deprecated item: prefer using indexing
Merge pull request #111 from bharrisau/systick

Minor changes to systick
Use rlibc crate
Merge pull request #113 from errordeveloper/rlibc

Use rlibc crate

Reviewed-by: farcaller
Fix for latest rustc.