Limit lines

Currently csvlint.rb reads all the lines of the CSV files which can become very long for large files while most of the issues will be discovered in the first 10,000 or 100,000 lines (in files with potentially millions of records).

The proposed change add a supported parameter (limitLines) in the configuration dialect to limit the maximum number of lines evaluated, allowing to control the execution duration. (could even be useful for the web instance csvlint.io where most users will think that no output will come.