Merge pull request #29 from bvssvni/master

Upgraded to latest Rust
Implement unsharpen masking

see:
https://en.wikipedia.org/wiki/Unsharp_masking#Digital_unsharp_masking

and

http://homepages.inf.ed.ac.uk/rbf/HIPR2/unsharp.htm

for details
Merge pull request #30 from ccgn/master

Implement unsharpen masking
Implement box filtering
Merge pull request #31 from ccgn/master

Implement box filtering
Upgraded to latest Rust-Empty