This PR updates OrderedDict’s C implementation, and adds insert_before, insert_after, and swap, which are discussed in the thread below.
https://discuss.python.org/t/insert-swap-get-by-index-for-ordereddict/52375/5

from collections import OrderedDict
d = OrderedDict({i:i for i in range(10)})
d = OrderedDict(a=1, b=2, c=3)
a = d.copy()
a.insert_before('b', 'x', 0)
print(dict(a))
b = d.copy()
b.insert_after('b', 'x', 0)
print(dict(b))
d.swap('a', 'c')
print(dict(d))