Add uvloop as Posix+CPython dependency and tweak new Make recipes (#2819)

- uvloop is now a dependency on non-Windows CPython systems
- `make setupenv` renamed to `make newenv`
- `make syncenv` added to sync local venv to current dependencies
- `dev-requirements.txt` moved into `tools` directory

setup.cfg

@@ -45,6 +45,7 @@ install_requires =
     Red-Lavalink==0.3.0
     schema==0.7.0
     tqdm==4.32.2
+    uvloop==0.12.2; sys_platform != "win32" and platform_python_implementation == "CPython"
     websockets==6.0
     yarl==1.3.0
 
@@ -63,7 +64,7 @@ docs =
     pytz==2019.1
     requests==2.22.0
     six==1.12.0
-    snowballstemmer==1.2.1
+    snowballstemmer==1.9.0
     Sphinx==2.1.2
     sphinx-rtd-theme==0.4.3
     sphinxcontrib-applehelp==1.0.1
@@ -88,13 +89,13 @@ test =
     isort==4.3.21
     lazy-object-proxy==1.4.1
     mccabe==0.6.1
-    more-itertools==7.0.0
+    more-itertools==7.1.0
     packaging==19.0
     pluggy==0.12.0
     py==1.8.0
     pylint==2.3.1
     pyparsing==2.4.0
-    pytest==4.6.3
+    pytest==5.0.0
     pytest-asyncio==0.10.0
     six==1.12.0
     typed-ast==1.4.0