Preserve DateTime microsecond precision

Makefile

@@ -3,6 +3,14 @@ SOURCES=$(shell find src -type f)
 build: $(shell find src -type f)
 	nimble build
 
+unittest:
+	nimble unittest
+.PHONY: unittest
+
+integrationtest:
+	nimble integrationtest
+.PHONY: integrationtest
+
 docs: $(shell find src -type f)
 	nim doc --project --index:on --git.url:https://github.com/jdbernard/fiber-orm --outdir:docs src/fiber_orm
 	nim rst2html --outdir:docs README.rst