+ xo-printable2 + build fixes for cmake config

README.md

@@ -1 +1,56 @@
 # xo-facet
+
+
+## Codegen
+
+To scaffold a new facet Foo we need several c++ classes
+
+* `AFoo`      abstract FOMO interface, with opaque data pointer
+* `IFoo_Any`  variant placeholder, all methods terminate
+* `IFoo_Xfer` template, delegates methods to a separate implementation class
+* `RFoo`      template, inherits from a 2x-wide fat pointer (iface+data).
+
+These classes all have parallel methods
+Can generate these as follows:
+
+1. write `xo-foo/idl/Foo.json5`.
+
+   Supply attributes:
+   - mode :: string
+   - includes :: [string]
+   - namespace1 :: string
+   - namespace2 :: string
+   - facet :: string
+   - detail_subdir :: string
+   - brief :: string
+   - using_doxygen :: bool
+   - doc :: [string]
+   - types :: [{name, doc, definition}]
+   - const_methods :: [{name, doc, return_type, args, const, noexcept, attributes}]
+   - nonconst_methods :: [{name, doc, return_type, args, const, noexcept, attributes}]
+
+Example in xo-object2/idl/Sequence.json5
+
+2. generate:
+
+```
+$ cd xo-foo
+$ ../xo-facet/codegen/genfacet.py --input ./idl/Foo.json5 --output include/xo/foo2
+```
+
+Alternatively in `xo-foo/CMakeLists.txt`
+
+```
+xo_add_genfacet(
+    TARGET xo-foo2-facet-foo
+    FACET Foo
+    INPUT idl/Foo.json5
+    OUTPUT_HTTP_DIR include/xo/foo2
+    OUTPUT_IMPL_SUBDIR detail
+    OUTPUT_CPP_DIR src/foo2)
+```
+
+then generate with:
+```
+cmake --build path/to/build -- xo-foo2-facet-foo
+```