Pattern builder

[RunDevelopment]

This PR is an implementation of #1476.

I decided to make a new namespace Prism.patterns (*hint* *hint* #1494) to keep things organized because build doesn't really belong in any of the other namespaces.

The validation method of the base pattern and replacements is located in a new file called tests/helper/prism-core-tester.js.
This file's purpose is to add testing functionality to existing Prism methods only when running npm test. This has the following advantages:

• prism-core.js stays small but still validates on all tested components.
• The validation is not done on our client's computers.

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Maybe we should make this a resource (#1539)?

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Btw. This and #1537 go together really well.

[RunDevelopment]

It intrigues me that the build failed despite the fact that I only changed some comments...

It seems like the npm install -g gulp command took longer than 10 minutes. How can that be?
Node v6 took each about 7 minutes for npm install and nom install -g gulp.

[RunDevelopment]

Now it worked again.
And it took at most 20 seconds for the npm install commands.

[mAAdhaTTah]

Travis does weird stuff sometimes. I wouldn't worry too much about it.

[RunDevelopment]

This is just an idea for now but with ES6 tagged template literals we could make a function Prism.regex which will behave like Prism.patterns.build but has a nice syntax:

const foo = /\bfoo\b/;

Prism.regex`\w\s${foo}\s`; // returns /\w\s(?:\bfoo\b)/

// instead of
Prism.patterns.build(/\w\s<<0>>/, [foo]);

There a few drawbacks (flags, browser compatibility, no regex syntax highlighting).
The fact, that the tag approach does not use regex literals is both an advantage (no regex compile overhead) and a disadvantage (syntax check only during runtime, no syntax highlighting).

Edit: Flags can be declared using regex (no flags), regex.i, regex.m, and regex.im.

[RunDevelopment]

Closed in favor of #2190.