chore: Use grep -E / grep -F instead of egrep / fgrep (#2164)

Ensures that the -E or -F option, when used, is the first option
* i.e. grep -oE => grep -E -o

Updates _bash-it-grep to invoke grep with just the provided arguments
* This function was (and still is) unused, but decided this new functionality was actually more useful

Introduces _bash-it-fgrep to invoke grep -F

Removes type -P egrep from the _bash-it-*grep functions

For usages that were already going to be modified, use -F if appropriate
* Does not touch grep usages that may have benefited from -F, but were not otherwise considered for this PR

Adds shellcheck header to modified .bash files that didn't already have it

completion/available/fabric.completion.bash

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 #
 # Bash completion support for Fabric (http://fabfile.org/)
 #
@@ -91,7 +91,7 @@ function __fab_completion() {
         -*)
             if [[ -z "${__FAB_COMPLETION_LONG_OPT}" ]]; then
                 export __FAB_COMPLETION_LONG_OPT=$(
-                    fab --help | egrep -o "\-\-[A-Za-z_\-]+\=?" | sort -u)
+                    fab --help | grep -E -o "\-\-[A-Za-z_\-]+\=?" | sort -u)
             fi
             opts="${__FAB_COMPLETION_LONG_OPT}"
             ;;
@@ -101,7 +101,7 @@ function __fab_completion() {
         # -*)
         #     if [[ -z "${__FAB_COMPLETION_SHORT_OPT}" ]]; then
         #         export __FAB_COMPLETION_SHORT_OPT=$(
-        #             fab --help | egrep -o "^ +\-[A-Za-z_\]" | sort -u)
+        #             fab --help | grep -E -o "^ +\-[A-Za-z_\]" | sort -u)
         #     fi
         #     opts="${__FAB_COMPLETION_SHORT_OPT}"
         #     ;;