* Refactor `PtcInfo`
This change reduces the coupling of `PtcInfo` by moving relocation
tracking to the backend. `RelocEntry`s remains as `RelocEntry`s through
out the pipeline until it actually needs to be written to the PTC
streams. Keeping this representation makes inspecting and manipulating
relocations after compilations less painful. This is something I needed
to do to patch relocations to 0 to diff dumps.
Contributes to #1125.
* Turn `Symbol` & `RelocInfo` into readonly structs
* Add documentation to `CompiledFunction`
* Remove `Compiler.Compile<T>`
Remove `Compiler.Compile<T>` and replace it by `Map<T>` of the
`CompiledFunction` returned.
