Add proguard rules

[RyanNewsom]

You should add proguard rules to your library so that consumers don't have to figure out what they need to be themselves. If you want to test this, turn on minifyEnabled on your sample app, it will crash.

Related to #10

[sinarostami]

Add below lines into the progaurd-rules.pro file:

-keep class org.walletconnect** { *;}
-keep class dev.pinkroom.walletconnectkit** { *; }