sage --package: Add commands "list :standard:", "update-latest" (for packages from PyPI), "upload"

[vbraun]

For pip-type packages we can get version information automatically from PyPI. This new subcommand downloads the latest tarball and updates package-version.txt and checksums.ini in one go:

$ sage --package update-latest matplotlib
Updating matplotlib: 1.5.0 -> 1.5.1
Downloading tarball to /home/vbraun/Code/sage.git/upstream/matplotlib-1.5.1.tar.bz2
[......................................................................]

Depends on #29890

Component: packages: optional

Author: Volker Braun

Branch/Commit: u/mkoeppe/automatic_updates_of_pip_type_packages @ a91ecab

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/20104

[vbraun]

Branch: u/vbraun/automatic_updates_of_pip_type_packages

[vbraun]

Commit: 55e6e02

[vbraun]

Author: Volker Braun

[vbraun]

New commits:

6852d4c	Use argparse in sage_bootstrap
8a6c664	Add sage --package download and fix-checksum
7332d26	Fix and deprecate sage-fix-pkg-checksums
443cf39	Correct helpstring
8fe1549	Also test sage --package update
0d7bd01	Merge #19984 into #20104
55e6e02	Add sage --package update-latest command

[vbraun]

Description changed:

--- 
+++ 
@@ -1 +1,8 @@
+For pip-type packages we can get version information automatically from PyPI. This new subcommand downloads the latest tarball and updates `package-version.txt` and `checksums.ini` in one go:
 
+```
+$ sage --package update-latest matplotlib
+Updating matplotlib: 1.5.0 -> 1.5.1
+Downloading tarball to /home/vbraun/Code/sage.git/upstream/matplotlib-1.5.1.tar.bz2
+[......................................................................]
+```

[vbraun]

Dependencies: #19984

[mkoeppe]

comment:4

needs rebase

[mkoeppe]

Changed branch from u/vbraun/automatic_updates_of_pip_type_packages to u/mkoeppe/automatic_updates_of_pip_type_packages

[mkoeppe]

Changed commit from 55e6e02 to 94ec3c9

[mkoeppe]

comment:7

Rebased on 9.2.beta1, not tested

---

New commits:

94ec3c9

Add sage --package update-latest command