HTTParty formatter, and truncate long Sequel strings

What's Changed

• Add HTTParty formatter by @rgalanakis in #10
  Use it like:

require 'appydays/loggable/httparty_formatter'
logger = SemanticLogger["my_app_logger"]
HTTParty.post("https://foo/bar", body: {x: 1}, logger: logger, log_format: :appydays)

• Truncate long Sequel logs by @rgalanakis in #10
  You can control this behavior, including the size cutoff, truncation message, context, and loging of the untruncated message. Refer to Sequel::Database::AppydaysLogger for information.

Full Changelog: 0.5.1...0.6.0