add alignTable, parseTableCells to align/format a tab(etc) delimited table (#10182)

* add compiler/unittest_light.nim for easy diffing: assertEquals and mismatch
* fixup
* add alignTable, parseTableCells

tests/compiler/nim.cfg

@@ -0,0 +1,7 @@
+# note: consider moving tests/compilerapi/ to tests/compiler/ since
+# that's more predictable.
+
+# note: without this, tests may succeed locally but fail on CI (it can succeed
+# locally even when compiling via `./bin/nim` because `$HOME/.nimble` is being
+# used).
+--path:"../../" # so we can `import compiler/foo` in this dir