Add support for properties files

Properties files are still used heavily in the Jvm world (which means java, scala, and tons of other languages). It would be nice if there was support for encrypting the values within a properties file. Property files are typically much simpler then yaml or json files. Every entry is a key/value pair separated by an = symbol. There are no dictionaries, lists, or any other type of tree structures within a properties file.

I haven't gone through the code base yet but how difficult do people believe it would be to add support for this filetype (and possibly other similar filetypes with different whitespace and seperate rules?)

A good looking project that supports reading and writing of properties file https://github.com/magiconair/properties using golang.
It has functions for retrieving all of the keys: https://godoc.org/github.com/magiconair/properties#Properties.Keys
Getting the value of a key:
https://godoc.org/github.com/magiconair/properties#Properties.Get
Setting a value of a key only if the key exists
https://godoc.org/github.com/magiconair/properties#Properties.MustSet
Forcing that certain keys must exist (good for making sure soaps related keys exist)
https://godoc.org/github.com/magiconair/properties#Properties.MustGet

The issue names no repository files, tests, or entry points. Start by reviewing the existing format-support approach and the referenced Go properties library, then define parsing and encryption behavior for key/value entries. Done means properties files can be supported while their values are encrypted and their key/value structure remains usable.