Add Boolean argument escape_csi to vim_feedkeys

- By default vim_feedkeys escaped all input for CSI/K_SPECIAL bytes
  before using it. However since vim_replace_termcodes() also escapes
  the input string chaining these functions together escapes input twice
- vim_feedkeys() now takes a third Boolean argument to enable/disable
  escaping
- Breaks API compatibility
Functional tests for feedkeys CSI escaping

- tests for vim_feedkeys and replace_termcodes
Merge PR #1270 'Add Boolean argument escape_csi to vim_feedkeys'