Allow project specific coverage ignore paths

[barlock]

Expected Behavior

As a user of sol-coverage I should be able to specify paths that I want to ignore from coverage so that I don't have to test my node_modules to get full test coverage.

Current Behavior

Right now, it just covers everything. Being able to ignore things allows me to ensure I can only focus on the code I want to.

Possible Solution

Intake a list of ignore paths, don't add those paths to the istanbul collector.

Context

This is getting run in a CI system with istanbul checking coverage.

Your Environment

Package	Version
@0x/sol-coverage	"^2.0.3"
@0x/sol-trace	"^2.0.4"

Network
NAME

[LogvinovLeon]

Two questions.

1. Would you be satisfied with just the boolean flag ignoreNodeModules (true by default) or do you need smth more complex than that?
2. If you do - would you prefer glob or regex?

[barlock]

I want something more complex. In my current use case, I'm actually having to copy ERC721 contracts into my project as they don't have a payable modifier on transfer. I don't want these covered either.

I have this currently hacked together in a project https://github.com/ConsenSys/web3studio-bootleg/pull/125/files#diff-234b5ebe98eaf702468d693d7031023eR27

☝️ It's implemented with globs because of simplicity, but I would prefer regex to match other ignore formats (nyc, Jest, git, etc).