scikit-hep/uproot4: 4.1.0

The main new feature in this release is that Uproot 4 can now write ROOT files. It is no longer necessary to use Uproot 3 for anything: Uproot 4's capabilities exceed Uproot 3's in all ways that are currently known to me. This was implemented in PRs #405, #406, #408, #409, #412, #414, #415, #416, #420, #421, and was described in Discussion #321. All the new functions are documented, and an overview is presented in the Getting Started Guide. Other updates for this release: @jpivarski removed warning when XRootD is installed but not used: PR #388. @chrisburr allowed XRootD version strings to be non-numeric (e.g. from a self-built copy of the library): PR #395. @bnavigator marked test 0220 with the network tag, since it uses the network: PR #396. @jpivarski handled dimensions in a leaf-list: #399. @jpivarski removed '@' fields from lazy Forms, fixing lazy TLorentzVector: PR #403. @klieret fixed links to source in Sphinx: PR #410. @jpivarski allowed Float16_t to have up to 32 bits: PR #411. @veprbl added support for reading TDatime: PR #407