Connect to boost-histogram and hist. (#46)

* Connect to boost-histogram and hist.

* Assign behaviors from any superclasses.

* Move imports for 'extras' dependencies to a submodule.

* Converted TH1F into NumPy histogram.

* 1D and 2D histograms can both be converted to NumPy format.

* Converts 1D histograms to boost-histogram.

* Figuring out what metadata is good.

* Resolved metadata question; added categorical bins.

* Exactly correct TProfile errors (all four cases).

* Wrangling API and duplication.

* Punt on interpretation of boost-histogram WeightedMean.

* Fix flake8 error.

* Every histogram type must have a 'values_errors'.

* Remember to skip the boost-histogram tests if you don't have boost-histogram.

tests/test_0045-lazy-arrays-1.py

@@ -23,6 +23,7 @@ def test_array_cast():
 
 
 def test_branch_pluralization():
+    awkward1 = pytest.importorskip("awkward1")
     with uproot4.open(skhep_testdata.data_path("uproot-Zmumu.root"))[
         "events/px1"
     ] as px1:
@@ -155,6 +156,7 @@ def test_awkward_pluralization():
 
 
 def test_dask():
+    awkward1 = pytest.importorskip("awkward1")
     dask_array = pytest.importorskip("dask.array")
     files = (
         skhep_testdata.data_path("uproot-sample-6.20.04-uncompressed.root").replace(
@@ -175,6 +177,7 @@ def test_dask():
 
 
 def test_daskframe():
+    awkward1 = pytest.importorskip("awkward1")
     dask_frame = pytest.importorskip("dask.dataframe")
     files = (
         skhep_testdata.data_path("uproot-sample-6.20.04-uncompressed.root").replace(