Add a forced grid mode

[meain]

Maybe we should add an option to force a grid mode. This combined with --blocks might end up being really powerful.

One example would be

$ lsd --grid --blocks name,size
appveyor.yml 3 KB     build.rs 1.3 KB   Cargo.lock 33 KB   Cargo.toml 1.1 KB
CHANGELOG.md 8.2 KB   ci       160 B    CODEOWNERS 25 B    LICENSE    11.1 KB
README.md    5.4 KB   src      384 B    target     192 B   tests      96 B

Alternate view

appveyor.yml 3 KB    build.rs 1.3 KB  Cargo.lock 33 KB  Cargo.toml 1.1 KB
CHANGELOG.md 8.2 KB  ci 160 B         CODEOWNERS 25 B   LICENSE 11.1 KB
README.md 5.4 KB     src 384 B        target 192 B      tests 96 B

[matterhorn103]

This would be good, I was trying to include the output of lsd in my fish prompt and lsd steadfastly refuses to use grid mode, even when I put it in the config file (if I put layout: tree in the config file it is picked up and respected).