Previously, we represented quantizer values as an owned `String` for
constructing various encoder commands, which is much slower and less
robust than representing the quantizer as an integral value. This has
been updated to represent the `q` and `n_threads` both as a `usize`, and
only convert to a `String` for formatting as needed.
Furthermore, several struct fields containing paths have been updated to
use a `PathBuf` or `&Path` instead of a `String`. These are the first
steps required to supporting non-UTF8 filenames on Windows and
Unix-based operating systems.
`run_vmaf_on_chunk`'s function signature has been update to take generic
arguments that satisfy `AsRef<Path>`, which allows the caller to save
themselves from creating a new `Path` if the original argument was a
`String`, for example.
* Do not represent the concatenation method as a string
* Fix pedantic clippy warnings
* Remove Cargo.lock from .gitignore
* Fix startup_check for ivf concatenation
* Add doc comment to `Args` for better help generation in Clap
* Use Display impl instead of directly using str::From for `Encoder` and `ConcatMethod`
* Do not unwrap the result of killing child processes
* Assert that VMAF calculation was successful
* Use more idiomatic Rust
