Add gitignore usage information, fix empty api calls

Added general usage information. Made sure gitignore api is never called
without any arguments.

Made script fzf aware -- if it finds fzf it can be invoked without
arguments, if it does not it will display usage information instead.

git/.local/bin/gitignore

@@ -9,11 +9,18 @@
 # Will *overwrite* any previous .gitignore file that exists in
 # current directory.
 #
+# When called without arguments will load all possible arguments
+# as fzf searchable list if fzf is in path.
+#
 # Enables completion for zsh in git/.config/shell/zshrc.d/_gitignore_completions.zsh
 
 __get_items() {
+  if [ "$1" = "" ]; then
+    echo "gitignore definition generation needs at least one argument."
+    exit 1
+  fi
   if [ "$savetofile" = "true" ]; then
-    __call_url "$@" | tee .gitignore
+    __call_url "$@" >>.gitignore
   else
     __call_url "$@"
   fi
@@ -25,22 +32,48 @@ __call_url() {
 }
 
 gitignore() {
+  if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
+    usage
+    exit 0
   # just print to stdout or save locally?
-  if [ "$1" = "-f" ]; then
+  elif [ "$1" = "-f" ] || [ "$1" = "--file" ]; then
     savetofile=true
     shift
   fi
 
   IFS=","
   if [ "$#" -eq 0 ]; then
-    for item in $(__get_items list); do
-      echo "$item"
-    done | fzf --multi --ansi | paste -s -d "," - |
-      { read -r result && __get_items "$result"; }
-    cat
+    if type fzf >/dev/null 2>&1; then
+      for item in $(__get_items list); do
+        echo "$item"
+      done | fzf --multi --ansi | paste -s -d "," - |
+        { read -r result && __get_items "$result"; }
+    else
+      usage
+    fi
   else
     __get_items "$@"
   fi
 }
 
+usage() {
+  printf "%s\n" \
+    "" \
+    " gitignore     Quickly generate a gitignore definition." \
+    "" \
+    " Usage: gitignore [-h] [vim] [linux] [javascript] [...]" \
+    "" \
+    " Arguments:" \
+    "" \
+    "     -h | --help       Print out this help." \
+    "" \
+    "     -f | --file       Append gitignore definition to .gitignore file" \
+    "                       instead of stdout." \
+    "" \
+    "     Arguments will be passed along to gitignore.io for parsing and " \
+    "     gitignore definition generation. By default only prints to stdout." \
+    "" \
+    ""
+}
+
 gitignore "$@"