Support converting update_all and delete_all.
Merge pull request #5 from xinminlabs/feature/3_convert_update_all_and_delete_all

Feature/3 convert update all and delete all
ignore t.index in rails/strong_parameter snippet
add ruby/fast_syntax snippet
fix ruby/fast_syntax snippet, to_value => to_source
use synvert-core 0.7.0
improve rails/convert_mailers_2_3_to_3_0 snippet
make use of Dir.glob param to avoid iterating multiple file patterns
Support converting destroy_all.
Merge pull request #7 from xinminlabs/feature/6_convert_destroy_all

Support converting destroy_all.
improve rails/convert_rails_root snippet

File.exists?(Rails.root.join('xxx'))
=>
Rails.root.join('xxx').exist?
support sent_on for rails/convert_mailers_2_3_to_3_0 snippet
polish rails/convert_mailers_2_3_to_3_0 snippet
polish rails/convert_rails_env snippet
Check attributes of schema.rb to decide whether to convert or not.