Require "ephem" instead of "pyephem"

Package has been renamed on pypi.org.

Also, ephem V3.7 doesn't work. We require 4.1.

TODO.md

@@ -1,6 +1,5 @@
 # To do
 
-Package `pyephem` is now called simply `ephem` in pypi.org.
 
 
 ## Debian packaging

docs_src/quickstarts/pip.md

@@ -26,7 +26,7 @@ your system:
     sudo apt update && sudo apt upgrade
     sudo apt -y install gcc
     sudo apt -y install python3-dev
-    # This makes the install of pyephem go more smoothly:
+    # This makes the install of ephem go more smoothly:
     python3 -m pip install wheel
     ```
 
@@ -36,7 +36,7 @@ your system:
     sudo yum update
     sudo yum install -y gcc
     sudo yum install -y python3-devel
-    # This makes the install of pyephem go more smoothly:
+    # This makes the install of ephem go more smoothly:
     python3 -m pip install wheel
     ```
 
@@ -274,7 +274,7 @@ You can also use pip to uninstall the dependencies, but first check that they
 are not being used by other programs!
 
 ```shell
-python3 -m pip uninstall pyserial pyusb CT3 Pillow configobj PyMySQL pyephem ephem -y
+python3 -m pip uninstall pyserial pyusb CT3 Pillow configobj PyMySQL ephem ephem -y
 ```
 
 Finally, if desired, delete the data directory:

pyproject.toml

@@ -65,7 +65,7 @@ configobj = "^5.0"
 # This is the renamed "Cheetah" package:
 CT3 = "^3.1"
 Pillow = ">=5.2"
-pyephem = "^3.7"
+ephem = "^4.1"
 PyMySQL = {extras = ["rsa"], version = "^1.0"}
 pyserial = "^3.4"
 pyusb = "^1.0.2"