git-crypt (#56)

* Configure Git attributes `filter` and `diff` to use `git-crypt` setup

Ensured to exclude Git specific `.gitattributes` and `.gitignore` files.

Epic GH-33
Depends on GH-35 GH-49
GH-48

<--------------------------------------------------------------------->

* Import trusted GPG keys for git-crypt

Initialized git-crypt for the repository with `git-crypt init`.

Added GPG keys of all core team members by running the
`git-crypt add-gpg-user --trusted --no-commit <ID>` command where
`--no-commit` flag prevents automatic commit of generated files while
`--trusted` assumes the GPG user IDs are trusted.

Epic GH-33
Depends on GH-35 GH-49
Resolves GH-48

.git-crypt/.gitattributes

@@ -0,0 +1,4 @@
+# Do not edit this file.  To specify the files to encrypt, create your own
+# .gitattributes file in the directory where your files are.
+* !filter !diff
+*.gpg binary

.gitattributes

@@ -7,7 +7,16 @@
 # References:
 #   https://git-scm.com/docs/gitattributes
 #   https://git-scm.com/book/en/v2/Customizing-Git-Git-Attributes#Keyword-Expansion
+#   https://github.com/AGWA/git-crypt
+#   https://www.gnupg.org
+#   https://wiki.archlinux.org/index.php/GnuPG
 
 # Automatically perform line feed (LF) normalization for files detected as text and
 # leave all files detected as binary untouched.
 * text=auto
+
+# +------------+
+# + Encryption +
+# +------------+
+.gitattributes !filter !diff
+.gitignore !filter !diff