docs: add a section somewhere that discusses how to translate certain special GAP syntax

[fingolfin]

E.g. GAP options: foo(arg : opt) can be translated to foo(arg ; opt=true).

Other examples:

• how to access G!.bla (getbangproperty etc.)
• how to access G.1 (getproperty(G, 1) ?)

Could also give a hint / reminder that strings need to be translated

This could e.g. be under Accessing GAP from Julia

[ThomasBreuer]

The examples above are mentioned/described in the manual section "Convenience adapters".
Would it be enough to modify the introduction of the section "Accessing GAP from Julia" such that it points to "Convenience adapters"? (I can create a pull request for that.)

[ThomasBreuer]

@fingolfin See pull request #922 for a proposal.

I do not see a good place for a hint about necessary conversions of strings (or large integers).

Perhaps also wrapped GAP functions should be mentioned in the documentation (together with a remark that they cannot be used in situations where GAP needs objects in the filter IsFunction).

Concerning GAP's IsBound, currently one can check for "boundness" (is there such a word?) of global variables and record components via hasproperty; for checking whether a list entry is bound, I see just GAP.Wrappers.ISB_LIST, which looks clumsy; what would be a Julia-like name for it?