Add .gitignore and remove .DS_Store

Previously, there was no .gitignore, which led to unwanted files being
tracked by git. Now a basic .gitignore has been added, and .DS_Store has
been removed.

Related-Issue: #24
Signed-off-by: Matt Langbehn <matthew.langbehn@gmail.com>

Author: mlangbehn

.DS_Store

@@ -0,0 +1,25 @@
+# Ignore Vim files
+[._]*.s[a-w][a-z]
+[._]s[a-w][a-z]
+Session.vim
+.netrwhist
+*~
+tags
+
+# Ignore macOS files
+*.DS_Store
+.AppleDouble
+.LSOverride
+._*
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk