Many small features like highlighting of cells and sending cell headers.

Major changes:
- Added support for other REPLs.
- File paths are now enclosed in "" to support paths with spaces.
- Add option to prefer external clipboard program over internal yank.
- Highlight cell headers by default.
- Add option to show cell headers when running cells.
- Add commands to insert cells and convert to Markdown cell.
- Sent "i Ctrl-C" to clear prompt by default instead of Ctrl-U.
- Add options to disable clearing of prompt.
- Add option to update __file__ variable when running cells.

Add regex, skip tags in execution, use built-in copy.

New features:
- Support for regex when defining tags.
- Tags (cell headers) are not included in the execution.
- Use Vim's built-in copy functionality if available, no need for
  external clipboard program.

Change default to use tags, add multiple tags, bugfixes

New features:
- Support for multiple tags ('# %%', '#%%', '# <codecell>', and '##'
  by default)

Bugfixes:
- Fix IPythonCellExecuteJump to not use verbose mode
- Make IPythonCell{Prev,Next}Cell more robust

New commands and features, some bugfixes, updates to README

New features:
- Support for macOS
- Clear current line before sending new line(s)
- If the cell is empty, send '# empty cell'

New commands:
- IPythonCellPrevCommand
- IPythonCellRestart
- IPythonCellExecuteCellVerbose
- IPythonCellExecuteCellVerboseJump

Bugfixes:
- Fix error when executing an empty cell

First publicly released version