Format the doc/conf.py file with Black (#41)

Ran black on `doc/conf.py` and added it to the `black` and `flake8` runs
in the main Makefile. Removed the setting of `sys.path` since we're
installing the packaged in edit mode so it should be importable without
that hack.

Inspired on fatiando/rockhound#87

Makefile

@@ -4,7 +4,7 @@ TESTDIR=tmp-test-dir-with-unique-name
 PYTEST_ARGS=--cov-config=../.coveragerc --cov-report=term-missing --cov=$(PROJECT) --doctest-modules --doctest-glob='*.rst' -v --pyargs
 LINT_FILES=setup.py $(PROJECT)
 BLACK_FILES=setup.py doc/conf.py $(PROJECT) tutorials
-FLAKE8_FILES=setup.py $(PROJECT)
+FLAKE8_FILES=setup.py doc/conf.py $(PROJECT)
 
 help:
 	@echo "Commands:"

doc/conf.py

@@ -38,7 +38,7 @@
     "examples_dirs": ["../tutorials"],
     # path where to save gallery generated examples
     "gallery_dirs": ["tutorials"],
-    "filename_pattern": "\.py",
+    "filename_pattern": r"\.py",
     # Remove the "Download all examples" button from the top level gallery
     "download_all_examples": False,
     # Sort gallery example by file name instead of number of lines (default)