Support prompt_pattern configuration name

[russtoku]

While the Conjure client docs say that there is a g:conjure#client#...#prompt_pattern global Vim variable that allows changing the prompt pattern of the REPL. It doesn't appear to exist.

:he conjure-client-python-stdio says:

 g:conjure#client#python#stdio#prompt_pattern
          Lua pattern to identify a new REPL prompt. This match signals to
          Conjure that the previous evaluation is complete and we're ready
          to submit more code as well as collect all output prior to the
          marker as the result.
          Default: ">>> "

When executing this at the Neovim command prompt:

:echo g:conjure#client#python#stdio#prompt_pattern

it results in:

E121: Undefined variable: g:conjure#client#python#stdio#prompt_pattern

Executing this at the Neovim command prompt:

:lua = vim.g["conjure#client#python#stdio#prompt_pattern"]

displays:

nil

This means that there is no conjure#client#python#stdio#prompt_pattern global variable to configure the Python client.

However, executing this at the Neovim command prompt:

lua = vim.g["conjure#client#python#stdio#prompt-pattern"]

displays:

">>> "

Looking at the code for the Python client confirms that there is prompt-pattern configuration item and it's default value is ">>> ".

This is due to Vimscript not accepting dash (-) as as part of a valid variable name.

It would be convenient if Conjure supported prompt_pattern to allow Neovim users to use:

• :echo g:conjure#client#python#stdio#prompt_pattern to display the prompt pattern.
• :let g:conjure#client#python#stdio#prompt_pattern = '%[%d+%]: ' to set it.