Add Arch source package core harness (#7)

Author: MaxGhenis

README.md

@@ -1,16 +1,27 @@
 """Arch source-data foundation.
 
-Arch owns source-backed facts, target inputs, and microdata ingestion. Modeling
-choices such as source reconciliation, aging, imputation, target activation,
-and calibration profiles belong in Microplex packages.
+Arch owns source artifacts, source-backed facts, constraints, provenance, and
+microdata ingestion. Modeling choices such as source reconciliation, aging,
+imputation, target activation, and calibration profiles belong in Microplex
+packages.
 """
 
 __all__ = [
+    "bundle",
     "client",
+    "concepts",
+    "consumer_contract",
+    "core",
+    "database",
     "facts",
+    "harness",
     "jurisdictions",
+    "mirror",
     "microdata",
     "normalization",
+    "source_package",
+    "store",
     "sources",
+    "suite",
     "targets",
 ]