Change parameter checks and other style fixes

This commits contains the following modifications:

- Change parameter checks from number of parameters (`$#`) to content length of
  each parameter ( `-z "$1"` ).
  A command called with an empty string in the first parameter *still* receives one
  parameter (`$# = 1`), while checking the string length will work either way.

- Change commands that may be aliased to use the builtin / non-modified
  command, using the 'command' prefix (e.g. `git` -> `command git`).

- Changed the initialization sequence of the plugin, from using a function
  to being inline in the script.
  It also uses the $0 parameter which is set when the script is sourced, and
  it contains the script filepath.
  Example: with command `source test.sh` -> in test.sh, `$0` will be 'test.sh'.

- Various style fixes, including missing space and some comments.

plugins/omz-bootstrap/lib/map.zsh

@@ -1,40 +1,40 @@
-mapdir=$ZSH/cache/omz-bootstrap
+mapdir="$ZSH/cache/omz-bootstrap"
 
 _map_init() {
-  mkdir -p $mapdir
+  command mkdir -p "$mapdir"
 }
 
 _map_put() {
-  [[ "$#" != 3 ]] && return 1
-  mapname=$1; key=$2; value=$3
+  [[ -z "$1" || -z "$2" || -z "$3" ]] && return 1
+  local mapname=$1; local key=$2; local value=$3
   [[ -d "${mapdir}/${mapname}" ]] || mkdir "${mapdir}/${mapname}"
-  echo $value >"${mapdir}/${mapname}/${key}"
+  echo $value > "${mapdir}/${mapname}/${key}"
 }
 
 _map_get() {
-  [[ "$#" != 2 ]] && return 1
-  mapname=$1; key=$2
+  [[ -z "$1" || -z "$2" ]] && return 1
+  local mapname=$1; local key=$2
   cat "${mapdir}/${mapname}/${key}"
 }
 
 _map_keys() {
-  [[ "$#" != 1 ]] && return 1
-  mapname=$1
+  [[ -z "$1" ]] && return 1
+  local mapname=$1
   for key ($mapdir/$mapname/*); do
     basename $key
   done
 }
 
 _map_exists() {
-  [[ "$#" != 2 ]] && return 1
-  mapname=$1; key=$2
+  [[ -z "$1" || -z "$2" ]] && return 1
+  local mapname=$1; local key=$2
   [[ -f "${mapdir}/${mapname}/${key}" ]] && return 0
 }
 
 _map_remove() {
-  [[ "$#" != 2 ]] && return 1
-  mapname=$1; key=$2
-  rm "${mapdir}/${mapname}/${key}"  
+  [[ -z "$1" || -z "$2" ]] && return 1
+  local mapname=$1; local key=$2
+  command rm "${mapdir}/${mapname}/${key}"
 }
-_map_init
 
+_map_init