On /categories, change the # per page to be 100
On /categories, change the # per page to be 100

We only have 37 top-level categories now, so this will show all
top-level categories on one page for the foreseeable future and make for
a better browsing experience.

Fixes #505.

rust-lang/crates.io,Susurrus/crates.io,Susurrus/crates.io,rust-lang/crates.io,steveklabnik/crates.io,steveklabnik/crates.io,rust-lang/crates.io,steveklabnik/crates.io,Susurrus/crates.io,steveklabnik/crates.io,rust-lang/crates.io,Susurrus/crates.io