Reorganize how clink settings are loaded

4bfdf04d59 moved all clink config files
to vendor/ and therefore the files in config/ were not used and .history
was also moved to vendor/.

The new arrangement uses `--script` to load our own clink.lua file which in
turn as the first thing loads the original clink.lua file. The user defined
files are again in config/. As clink regenerates these files, if they are not
present, this also means that we don't need to include the settings file
in the git repo and therefore don't overwrite it on updates.

config/settings

@@ -1,43 +0,0 @@
-# name: Ctrl-D exits
-# type: bool
-# Ctrl-D exits the process when it is pressed on an empty line.
-ctrld_exits = 1
-
-# name: Ctrl-C raises exception
-# type: bool
-# When Ctrl-C is pressed Clink will pass it thourgh to the parent by raising the
-# appropriate exception.
-passthrough_ctrlc = 1
-
-# name: Esc clears line
-# type: bool
-# Clink clears the current line when Esc is pressed (unless Readline's Vi mode
-# is enabled).
-esc_clears_line = 1
-
-# name: Match display colour
-# type: int
-# Colour to use when displaying matches. A value less than 0 will be the
-# opposite brightness of the default colour.
-match_colour = -1
-
-# name: Executable match style
-# type: enum
-# Changes how Clink will match executables when there is no path separator on
-# the line. 0 = PATH only, 1 = PATH and CWD, 2 = PATH, CWD, and directories. In
-# all cases both executables and directories are matched when there is a path
-# separator present.
-exec_match_style = 2
-
-# name: Prompt colour
-# type: int
-# Surrounds the prompt in ANSI escape codes to set the prompt's colour. Disabled
-# when the value is less than 0.
-prompt_colour = -1
-
-# name: Auto-answer terminate prompt
-# type: enum
-# Automatically answers cmd.exe's 'Terminate batch job (Y/N)?' prompts. 0 =
-# disabled, 1 = answer 'Y', 2 = answer 'N'.
-terminate_autoanswer = 0
-