Audit consumer proguard rules

[samtstern]

cc @ashwinraghav who has been helping a developer debug a proguard issue

In #573 the following lines were introduced to the consumer proguard rules:

// REMOVED
-dontwarn retrofit.**		
-dontwarn retrofit2.**		

// ADDED
-dontnote retrofit2.Platform
-dontnote retrofit2.Platform$IOS$MainThreadExecutor
-dontwarn retrofit2.Platform$Java8

Ashwin changed them to this in a branch that seems to solve the developer's issue:

-dontwarn okio.** #safe
-dontwarn retrofit2.Call #safe
#-dontnote retrofit2.Platform #unsafe
#-dontnote retrofit2.Platform$IOS$MainThreadExecutor
-dontwarn retrofit2.Platform$Java8 #safe

Ashwin can you explain what the issue was?

[SUPERCILEX]

As a side note, this is Retrofit v2.3.0's suggested config:

# Platform calls Class.forName on types which do not exist on Android to determine platform.
-dontnote retrofit2.Platform
# Platform used when running on Java 8 VMs. Will not be used at runtime.
-dontwarn retrofit2.Platform$Java8
# Retain generic type information for use by reflection by converters and adapters.
-keepattributes Signature
# Retain declared checked exceptions for use by a Proxy instance.
-keepattributes Exceptions

[samtstern]

This has been fixed and released in version 3.2.2.