container: root: change base path, related refactor

The base path is now *outside* of the macro directory; allowing for a
more integrated view of `dfi`'s entire `root` system. This is more
apparent once running an interactive session where the expectation is
(more intuitively) that any path should be relative to 'src/root' and
not 'src/root/macro'.

The rationale for why this was in 'src/root/macro' to begin with stems
from how `root` (by default) will automatically load rootlogon.C in the
directory that `root` is started. This is causing more confusion than
not because `dfi`'s usage of `root` is not limited to macros.

These changes skirt the line between needing a major API bump and not
but, so far, appears to be on the side of *not*. However, the TODOs
noted for macro loading should be addressed prior to any API changes.

container/src/root/test/unit/utility.hh

@@ -373,7 +373,9 @@ TEST_F(CommonRepoFiles, MacroLoad)
   ASSERT_NE(ecode, nullptr);
   EXPECT_NE(*ecode, EErrorCode::kNoError);
 
-  ASSERT_NO_THROW(::dfi::macro::load("crypto/hash.C"));
+  // TODO(afiore): macro loading should not need to be prepended with "macro/"
+  //   (see TODO in common impl regarding plugins-like functionality)
+  ASSERT_NO_THROW(::dfi::macro::load("macro/crypto/hash.C"));
   gInterpreter->ProcessLine(
       "dfi::macro::common::crypto::botan::Hash h;", ecode.get());
   ASSERT_NE(ecode, nullptr);