Add color values in multiple data file formats

Previously the color values were only provided through the documentation
in the `README.md` file that can not be simply parsed programmatically
for automated usage in other projects.
This has been changed by adding the following data file formats that can
be parsed:

- JSON (1) - The file provides an object that contains an `colors`
  collection/array that stores the individual color HEX (2) values.
  They can be read and concatenated with a commato match Slack's
  shareable theme format.
- YAML (3) - Like the JSON format, the YAML file also provides the
  `colors` collection/array containing the color HEX values.
- Plain Text - The colors are also provided as plain text using a `.txt`
  file (4).

References:
  (1) https://json.org
  (2) https://en.wikipedia.org/wiki/Web_colors#Converting_RGB_to_hexadecimal
  (3) https://yaml.org
  (4) https://en.wikipedia.org/wiki/Text_file

Resolves GH-6

colors.json

@@ -0,0 +1,3 @@
+{
+  "colors": ["#2E3440", "#3B4252", "#88C0D0", "#2E3440", "#3B4252", "#D8DEE9", "#A3BE8C", "#81A1C1"]
+}

colors.txt

@@ -0,0 +1 @@
+#2E3440,#3B4252,#88C0D0,#2E3440,#3B4252,#D8DEE9,#A3BE8C,#81A1C1

colors.yml

@@ -0,0 +1,9 @@
+colors:
+  - "#2E3440"
+  - "#3B4252"
+  - "#88C0D0"
+  - "#2E3440"
+  - "#3B4252"
+  - "#D8DEE9"
+  - "#A3BE8C"
+  - "#81A1C1"