Version 0.3.0

• Verbs can now be used without start_expr/chain/end_expr with some considerations, check the
  updated vignettes (#3). Importantly, this makes table.express conflict with dtplyr.
• Fixed a bug that prevented automatically built chains to work after a left_join.
• The *_sd verbs now support lambdas as formulas (#19).
• Added max_by and min_by verbs.
• mutate_sd gained parameter .pairwise.
• distinct gained parameters .keep and .n.
• transmute gained parameter .enlist (#20).
• filter_on now allows empty names for data tables that already have keys (#17).
• All filtering verbs now have a which parameter (#17).
• Added nest_expr for certain scenarios that need the captured data.table; check the vignette
  (#16).
• Simplified semi_join.