Core macros for Psibase

This defines the core functions that back the macros for the fracpack crate and psibase crate. See the documentation for those crates.

Service macro test suite

There are 2 parts to the suite.

• Unit testing, which largely tests boundary conditions and failure cases.Run cargo test in the ./psibase-macros-lib/ subdir.
• functional testing (kinda) which exercises the service after it is transformed by the macro. Run cargo-psibase test in ../test_psibase_macros.