Abstract conversion error
Add annotations to records of less accurate #have conversion
Add annotations to records of less accurate #=~ conversion
Refactor handling of Report
Display cautions for less accurate conversions

Like the following:

    The `have(1).conversion_error` has been converted but it might possibly be incorrect due to a lack of runtime information. It's recommended to review the change carefully.
    spec/transpec/converter_spec.rb:123:          converter.report.should have(1).conversion_error

This closes #42.
Add a note about #have matcher to the -s/--skip-dynamic-analysis section

Related to #42.
Merge branch 'caution-for-less-accurate-conversion'