Various colClasses enhancements

NEWS.md

@@ -21,6 +21,7 @@
     * Detects GB-18030 and UTF-16 encodings and in verbose mode prints a message about BOM detection.
     * Detects and ignores trailing ^Z end-of-file control character sometimes created on MS DOS/Windows, [#1612](https://github.com/Rdatatable/data.table/issues/1612). Thanks to Gergely Daróczi for reporting and providing a file.
     * Added option `logical01` to read a column of only `0`s and `1`s as `logical`, default `TRUE` for convenience in most cases. The large sample of rows throughout the file means that `fread` will be confident that the column really does just contain `0`s and `1`s, enabling and encouraging this convenient and efficient choice to save needing conversion afterwards or setting `colClasses` manually. In R, `logical` is `integer` anyway and can be treated as such in calculations. Further, it is no longer allowed to have mixed-case literals within a single column; i.e., a column of `TRUE/FALSE`s is ok, as well as `True/False`s and `true/false`s, but mixing different styles together is not.
+    * `colClasses` now emits a warning if an invalid/unsupported type is specified: [#1634](https://github.com/Rdatatable/data.table/issues/1634). Thanks to @hughparsonage for the pull request.
     * Added ability to recognize and parse hexadecimal floating point numbers, as used for example in Java. Thanks for @scottstanfield [#2316](https://github.com/Rdatatable/data.table/issues/2316) for the report.
     * Now handles floating-point NaN values in a wide variety of formats, including `NaN`, `sNaN`, `1.#QNAN`, `NaN1234`, `#NUM!` and others, [#1800](https://github.com/Rdatatable/data.table/issues/1800). Thanks to Jori Liesenborgs for highlighting and the PR.
     * If negative numbers are passed to `select=` the out-of-range error now suggests `drop=` instead, [#2423](https://github.com/Rdatatable/data.table/issues/2423). Thanks to Michael Chirico for the suggestion.