added plugin for displaying prompt responsively

(cherry picked from commit 25a04de1e51358fc8b119c047343a060ee34ced6)
(cherry picked from commit 3f47be12e38c82d09ddaa4ba59269fa642d18840)

plugins/responsive-prompt/README.md

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+# Responsive Prompt
+
+`Responsive Prompt` is a `OhMyZSH` plugin, which makes your prompt
+responsive to your terminal's column size. It does so, by watching
+`$COLUMNS` environment variables. When it changes, this plugin reloads
+your ZSH prompt.
+
+## Different Prompts
+
+You can define several prompts for your terminal via functions named
+like `_prompt_60`, which defines the prompt to be used when `$COLUMNS`
+is greater than `60`. Note that, you must set `$PROMPT_BREAKPOINTS`
+variable, appropriately, for this to work. Example:
+
+    PROMPT_BREAKPOINTS=(100 50 0)
+    _prompt_100(){ PROMPT="<prompt1>"; }  # prompt when $COLUMNS > 100
+    _prompt_50() { PROMPT="<prompt2>"; }  # prompt when 100 >= $COLUMNS > 50
+    _prompt_0()  { PROMPT="<prompt3>"; }  # prompt when  50 >= $COLUMNS > 0
+
+You can, even, define different prompts using conditional statements in
+your `$PROMPT_FILE`. In this case, your `$PROMPT_FILE` will be sourced,
+whenever the value of `$COLUMNS` change, to reload your prompt. Example:
+
+    if [[ $COLUMNS -gt 100 ]]; then
+      PROMPT="<prompt1>"
+    elif [[ $COLUMNS -gt 50 ]]; then
+      PROMPT="<prompt2>"
+    else
+      PROMPT="<prompt3>"
+    fi
+
+## Variables
+
+- **`PROMPT_FILE`**: File which will be sourced (in order to reload the
+  `PROMPT`), if no appropriate prompt-setting functions were found.
+  Since, most ZSH users will have prompt defined somewhere inside their
+  `~/.zshrc` file, it is the default. However, if you have a dedicated
+  file for your prompt, you can specify it with this option, which will
+  speed up prompt rendering.
+
+- **`PROMPT_BREAKPOINTS`**: If you use prompt-setting functions, you can
+  use this variable to define the various `$COLUMNS` values, when the
+  plugin should reload your prompt. Note that, you must define this
+  variable in a decreasing array format. Default value: `(120 90 60 0)`,
+  which means that when `$COLUMNS` is greater than `120`, `_prompt_120`
+  function will be called, and so on. If the plugin is unable to find
+  a function by these names, your `$PROMPT_FILE` will be sourced to
+  reload the prompt.
+
+
+- **`PROMPT_NEWLINE_AFTER`**: If you prefer to break your prompt into
+  a multi-line prompt when it exceeds a given display length, you can
+  use this variable to specify such length. Once the prompt exceeds this
+  length, a newline character will be inserted in the variable
+  `$prompt_newline`, which you can use inside your prompt definition.
+  Otherwise, this variable will remain empty.