~joshleeb/euler

Add missing test to problem 4
Solve problem 10
Minor fix to spacing of comments for problems
Add module common::collatz with iterator over the Collatz sequence
Add rustfmt config and format
Add link to Fibonacci struct docs for p002
Solve problem 4 and add common/digits mod
Update main to handle multiple impls of Solve trait
Add common module with an iterator over the Fibonacci Sequence
Run problem selected from env::args if provided
Move Solve trait into solve mod
Add solve_elapsed fn to Solve trait with default impl
Add documentation and tests for p001::Problem
Add Cargo.lock to gitignore
Initial Cargo project setup