The `string.gsub()` function in Lua always uses Lua patterns (which aresimilar to regular expressions).  Cmder's custom prompt wants to performsimple plain text find/replace operations on strings.  `string.gsub()`is the right Lua function for that, but since it always uses Luapatterns it's necessary to apply escaping to the input strings otherwisethey can get misinterpreted and cause runtime errors.For example, if the current working directory name contains a percentsign, such as literally "My%20Home".This change fixes that.  It introduces a helper function `gsub_plain()`which behaves like `string.gsub()` but applies appropriate escaping toconvert the plain text input strings into the corresponding Luapatterns so that it can achieve plain text find/replace operations.It also introduces separate helper functions for escaping the `find` and`replace` parameters for `string.gsub()`, since they have differentescaping rules.