Added timeouts and instrumentation for Excon

Adds retry on compatibility check requests

Merge pull request #12 from meetcleo/add-thread-safe-cache

move to thread-safe map

Merge pull request #11 from meetcleo/optimizations

optimize encode

Merge pull request #10 from meetcleo/expose-cache-fix

Expose cache and fix bool params

Merge pull request #8 from meetcleo/refresh-connections

add headers on-the-fly at each call

Merge pull request #7 from meetcleo/add-connection-pooling

add connection pooling

Merge pull request #6 from meetcleo/1.9.1

Add retries to 1.9.0