API document

[guybedford]

It's time to create a docs/api.md file as the readme has reached its limits.

[guybedford]

• Custom fetch hook in builder (eg https://github.com/systemjs/builder/pull/373/files#diff-04c6e90faac2675aa89e2176d2eec7d8R264)
• Conditional loading
• Incremental builds (eg https://github.com/systemjs/builder/pull/374/files#diff-04c6e90faac2675aa89e2176d2eec7d8R286)
• SFX disable encodings
• Note how normalization spaces work, that it is a URL space
• Source maps options, including lowResSourceMaps
• How build cache works, when to use reset etc.
• How to use simple bundles (Document how to include bundles #348)
• Plugin build hooks (Document plugin build hooks #420)
• Getting list of modules in a build (Determine which modules are in a bundle #390)
• Note babel 5 / Babel 6 support (the build example in this documentation is not working #463)
• output.modules for injecting bundle config
• builder.reset() cache use
• individual file invalidate API

[guybedford]

Along with conditional loading, we need to link the conditional not resolved error to the doc page on how to set conditions comprehensively (#504).

[ainscore]

Is this something that can be started on? I'd be interested in putting up a first draft.