docs/reference/dom-specific: adding domain specific language features

[soypat]

Create a new section under reference called Domain specific features to dump all technical details about features added to tinygo which are not present in Go or that function differently such as:

• pragmas
• Stdlib functionality (what does it mean to not have an OS?)
• Memory addresses of microprocessor peripherals

I am available for starting work on this if I get a greenlight!

Below is data exchanged on slack channel.

Benjamin Gould:
function pragmas: https://github.com/tinygo-org/tinygo/blob/release/compiler/symbol.go#L245-L296
global pragmas: https://github.com/tinygo-org/tinygo/blob/release/compiler/symbol.go#L430-L453

Ayke:
The //go:inline pragma is only a hint. It will make it more likely that something is inlined, but it's no guarantee at all. In fact, I would very much recommend against using it unless you know what you're doing: the compiler usually knows better whether to inline a function or not.
The compiler will already inline many functions, the pragma only makes it somewhat more likely.

• //go:inline and //go:noinline: only for very specific cases. Makes inlining more likely, does not have an effect on heap allocations.
• //go:linkname: same as regular Go, don't use it unless you know what you're doing.
• //go:align and //go:section: only for specific use cases like DMA.
• //go:nobounds: unsafe, don't use unless you know what you're doing
• //go:variadic: don't use (only for internal use)
• //go:export: alias for //export, the only pragma that is meant for use in regular code