[#2] Functions for reading maven settings.xml and decoding passwords

[ieugen]

• This should allow people to use maven encrypted passwords
• Addresses #2

[slipset]

Hey, I'm being a bit picky here, I hope that's ok. If you want to do this less async, feel free to hit me up on the clojurians slack where my nick is also @slipset

[ieugen]

I pushed some changes. I ended up keeping the Settings parameter - mostly for consistency.