save a call to Map.get by iterating entries
copy map of structs to create before iteration

In case of nested structs like "(b(oss))", structs_to_create could be
modified while it is currently iterated. This violates assertions in
libgee and crashes the program. Iterate over a copy instead, then
continue iterating with the difference set to create nested structs.
accept "read" as a valid access type as well
treat access modifier "read" as "readonly"

Some descriptions use just "read" to mean "readonly". It is unambiguous
enough to assume their equivalence.
Merge pull request #1 from dffischer/recursive-structs

Support recursive structs
Merge pull request #2 from dffischer/readonly

support "read" as an access modifier
update configuration for newer libgee

This revision will not compile. Further commits will restore
functionality by modification of the sources to use the newer API.

Conversely, libgee-0.8 is indeed newer than libgee-1.0. The projects
homepage <https://wiki.gnome.org/action/show/Projects/Libgee> states
under "Versions": "From version 0.1 to 0.6 the suffix for the libgee was
1.0 even though the API and ABI was not always kept stable."
remove functions from map and set constructors

The new libgee creates the adequate functions automatically.

This commit restores correct compilation.