switch CLI to using click, handles printing colors

docs for click are good, would recommend skimming over them
https://click.palletsprojects.com/en/7.x/#documentation

everything is backwards-compatible with the previous
interface, the only minor changes were to the doctor cmd
which can now accept more than one item to run,
and the --skip-config-check to skip the config_ok
check if the user specifies to

added a test using click.testing.CliRunner (tests
the CLI in an isolated environment), though
additional tests which aren't testing the CLI
itself (parsing arguments or decorator behaviour)
can just call the functions themselves, as they
no longer accept a argparser.Namespace and instead
accept the direct arguments

my/core/warnings.py

@@ -9,6 +9,9 @@ import sys
 from typing import Optional
 import warnings
 
+import click
+
+
 # just bring in the scope of this module for convenience
 from warnings import warn
 
@@ -18,16 +21,11 @@ def _colorize(x: str, color: Optional[str]=None) -> str:
 
     if not sys.stdout.isatty():
         return x
+    # click handles importing/initializing colorama if necessary
+    # on windows it installs it if necessary
+    # on linux/mac, it manually handles ANSI without needing termcolor
+    return click.style(x, fg=color)
 
-    # I'm not sure about this approach yet, so don't want to introduce a hard dependency yet
-    try:
-        import termcolor # type: ignore[import]
-        import colorama # type: ignore[import]
-        colorama.init()
-        return termcolor.colored(x, color)
-    except:
-        # todo log something?
-        return x
 
 def _warn(message: str, *args, color: Optional[str]=None, **kwargs) -> None:
     stacklevel = kwargs.get('stacklevel', 1)