C++ coding style is not documented

[sbc100]

Ran into this issue when reviewing some recent additions.

Currently the only documentation I could find was that we specify BasedOnStyle: Chromium in .clang-format. This implicitly locks down a lot of things which good, more explicit docs would be good.

The specific issue we ran into was the wabt uses a style that requires curly braces around conditional blocks, but chromium, which inherits from google style allows from single line conditional, and conditional without curlys:
https://google.github.io/styleguide/cppguide.html#Conditionals
In general, curly braces are not required for single-line statements

We should be specific if we want to enforce this style.

[sbc100]

@binji @aardappel

[binji]

Yeah, I had a warning for missing curly braces I think, but maybe it's not triggering anymore...? In any case, it would be better to be clear about this. However, AFAIK it's not possible in the .clang-format file, since it generally only adds/removes whitespace.

[sbc100]

What do you think about relaxing the style to match chomium's :)

[sbc100]

Should we add a paragraph about the style guidelines to Contributing.md?

[binji]

IIRC, I switched to requiring braces because it seemed like most folks preferred it.

Contributing.md seems like a reasonable place, yeah.