pull things that aren't JavaScript specific into a separate section

[dbaron]

Before I work on #126, I'd like to do a little bit of restructuring to separate parts of the design-principles document that are specific to JavaScript from parts that are cross-language.

In particular, we currently have the following two toplevel sections:

• JavaScript Language
• API Surface Concerns

What I'd like to do is rename the latter "API Surface Concerns" to "Javascript API Surface Concerns", and at the same time pull 4 of its subsections:

• Naming things
• New features should be detectable
• Use casing rules consistent with existing APIs
• Consider limiting new features to secure contexts

into a new toplevel section, perhaps called "API Design Across Languages", and put this before the "JavaScript Language" section. When doing this I'd also swap the order of the middle two so that the two naming-related subsections "Naming things" and "Use casing rules consistent with existing APIs" would be next to each other.

Does this seem reasonable?

[hober]

Sounds good to me!