* headers plugin
* Remove plugin
* Add non-functioning headers command
* Add ability to extract headers from first row
* Refactor header extraction
* Rebuild indexmap with proper headers
* Rebuild result properly
* Compiling, probably wrapped too much?
* Refactoring
* Deal with case of empty header cell
* Deal with case of empty header cell
* Fix formatting
* Fix linting, attempt 2.
* Move whole_stream_command(Headers) to more appropriate section
* ... more linting
* Return Err(ShellError...) instead of panic, yield each row instead of entire table
* Insert Column[index] if no header info is found.
* Update error description
* Add initial test
* Add tests for headers command
* Lint test cases in headers
* Change ShellError for headers, Add sample_headers file to utils.rs
* Add empty sheet to test file
* Revert "Add empty sheet to test file"
This reverts commit a4bf38a31d.
* Show error message when given empty table
This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).
