changes from the branch `bootstrap' excluding the bootstrapped interpreter itself
 - interpreter distinguishes between standard primitive operators and special forms
 - added dynamic loading, including export of c symbols
 - added variable-length parameter lists
 - added printing objects to strings
 - added modulo operator
 - added convenience function for making error objects
 - primitives are raw pointers again (no longer wrapped)
 - identifiers can contain colons now
 - cosmetic fixes for debugging
 - small bugfixes/enhancements for potato functions