Improve plotting of self-loops

[Silmathoron]

This is a proposal to update the way self-loops are currently plotted.
I find the current plot slightly strange since the arrow does not end on the node and the loop does not rescale upon zoom contrary to the other edges.

Since drawing correct circles is complex and error prone, I propose to reshape the loops as triangles and scale them based on node or edge size.

import networkx as nx
import matplotlib.pyplot as plt

g = nx.DiGraph()

g.add_nodes_from(range(5))

g.add_edges_from(
    [(0, 0), (0, 1), (1, 2), (2, 0), (2, 2), (2, 3), (3, 1), (3, 4), (4, 4)])

fig, axes = plt.subplots(2, 2)

ns = [40, 80, 60, 100, 120]
es = [5, 1, 2, 3, 1, 5, 5, 4, 2]

h = nx.Graph()
h.add_node(0)
h.add_edge(0, 0)

nx.draw(g, ax=axes[0, 0], node_size=ns)
nx.draw_circular(g, ax=axes[0, 1], node_size=ns[::-1])
nx.draw_shell(g, ax=axes[1, 0], node_size=ns, width=es)
nx.draw(h, ax=axes[1, 1])

plt.show()

There is still one thing i did not figure out, which is how to prevent them from getting out of the view... any help on that side would be appreciated.