Generate some more code to reduce code duplication and table sync issues

[fingolfin]

In Singular 4.1, they added some new types, including smatrix and cring. We probably will want to support those eventually. Right now, adding support for a new Singular type foobar is very cumbersome, as it involves at least changing the following (and more if we actually want to provide useful functions for those types):

• src/singtypes.h: add SINGTYPE_FOOBAR and SINGTYPE_FOOBAR_IMM to enum SingType
• src/singtypes.h: update GAPtoSingType, and HasRingTable (and ensure HasRingTable stays in sync with its counterpart in src/gen_highlevel_mappings.g); and also add ExportAsRecEntry(SINGTYPE_FOOBAR) in `InitSingTypesFromKernel()
• lib/libsing.gd and lib/libsing.gi: add constructor SI_foobar`
• lib/singtypes.gd: call DeclareCategory, create GAP types and put them into _SI_Types
• lib/singtypes.gi: add a _SI_TypeName method
• optionally (but recommended): lib/view.gi: add View methods
• src/gen_highlevel_mappings.g: add foobar to IsRingDep and possibly singularConstructors
• ... ?

A lot of that could be generated by a script from a single source file. That could then also do additional things; e.g. it would be nice if we also had a way to map Singular enum values like STRING_CMD to strings (e.g. "STRING_CMD") and back; then this can be used to add helpful comments in generated code and for other debugging purposes.

[hannes14]

libSingular provides Tok2Cmdname
(const char * Tok2Cmdname(int tok) in Singular/ipshell.h)
which converts STRING_CMD to "string", int('+') to "+", etc.
The other way is provided by IsCmd
(int IsCmd(const char *n, int & tok); in Singular/ipshell.h)
return for IsCmd("string",t) STRING_CMD (and sets t to ROOT_DECL_LIST)

[fingolfin]

Beautiful, thank you, that makes some of these things a lot easier.

[fingolfin]

OK, I just realized that I am actually aware of these, and we are using them -- what I meant is that I really want the string "STRING_CMD" as output for the input value STRING_CMD. But that, too, shouldn't be too hard to set up.