add lionel export builder with DSL

DSL can be used to map card data to arbitrary Google Doc columns:

Lionel.export do
  A { id }
  B { name }
  C { url }
end
replace export configuration with DSL usage loaded by default
use instance_exec to pass referent to export in column blocks
README
update README
remove unused error handling and auto-loaded export configuration
example export config
ensure authorization works during dry run export
default export builder method
consolidate logging code
extend expiration of google refresh token
evaluate Lionelfile given via command line to configure export builder
Merge pull request #1 from rossta/dsl

DSL for describing export columns