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/macro/test/benchmark.C

@@ -66,9 +66,9 @@ class Benchmark
   {
     static bool loaded{false};
     static const std::initializer_list<std::string> paths{
-        {"../test/benchmark/hash.hh"},
-        {"../test/benchmark/random.hh"},
-        {"../test/benchmark/utility.hh"}};
+        {"test/benchmark/hash.hh"},
+        {"test/benchmark/random.hh"},
+        {"test/benchmark/utility.hh"}};
 
     if (!loaded)
       {

container/src/root/macro/test/unit.C

@@ -66,10 +66,10 @@ class Unit
   {
     static bool loaded{false};
     static const std::initializer_list<std::string> paths{
-        {"../test/unit/hash.hh"},
-        {"../test/unit/random.hh"},
-        {"../test/unit/type.hh"},
-        {"../test/unit/utility.hh"}};
+        {"test/unit/hash.hh"},
+        {"test/unit/random.hh"},
+        {"test/unit/type.hh"},
+        {"test/unit/utility.hh"}};
 
     if (!loaded)
       {