Update some Python machinery, create sass tools

tools/python/defs.bzl

@@ -158,6 +158,7 @@ py_resources = rule(
 def py_project(name=None,
                main=None,
                main_deps=None,
+               main_data=None,
                shebang=None,
                lib_srcs=None,
                lib_deps=None,
@@ -218,6 +219,7 @@ def py_project(name=None,
             name=name,
             main=main,
             deps=(main_deps or []) + [lib_name],
+            data=(main_data or []),
             imports=[
                 "src/python",
                 "src/resources",

tools/python/requirements.in

@@ -17,6 +17,7 @@ icmplib
 isort
 jinja2
 lark
+libsass
 livereload
 lxml
 markdown

tools/python/requirements_lock.txt

@@ -39,6 +39,7 @@ jsonschema==4.17.3
 jsonschema-spec==0.1.4
 lark==1.1.5
 lazy-object-proxy==1.9.0
+libsass==0.22.0
 livereload==2.6.3
 lxml==4.9.2
 Markdown==3.4.3