Merge comp into plug

[Granddave]

Fixes #17

I tried to merge the two functions but am not sure that zapcomp really worked before.
There are two fpath+= but I guess that only one is needed? I.e. this one: fpath+=$("$completion_file_path"), and scrap fpath+="$(dirname "$plugin_dir")"..?

I am also not sure that this kind of variable operation ${completion_file:1} is valid POSIX, so changing #!/bin/sh to #!/bin/zsh (or just remove the shebang since it's not supposed to be run anyway) would be better.

Also, updated the way download progress is shown. Now the plug is shown during the download and when it's finished the icon will change to the lightning bolt :)

[ChristianChiarulli]

export ZAP_DIR="$HOME/.local/share/zap"
export ZAP_PLUGIN_DIR="$ZAP_DIR/plugins"

function _try_source() {
    # shellcheck disable=SC1090
    [ -f "$1" ] && source "$1"
}

function zapplug() {
    local full_plugin_name="$1"
    local initialize_completion="$2"
    local plugin_name=$(echo "$full_plugin_name" | cut -d "/" -f 2)
    local plugin_dir="$ZAP_PLUGIN_DIR/$plugin_name"
    if [ ! -d "$plugin_dir" ]; then
        echo "🔌$plugin_name"
        git clone "https://github.com/${full_plugin_name}.git" "$plugin_dir" > /dev/null 2>&1
        if [ $? -ne 0 ]; then
            echo "Failed to install $plugin_name"
            exit 1
        fi
        echo -e "\e[1A\e[K⚡$plugin_name"
    fi
    _try_source "$plugin_dir/$plugin_name.plugin.zsh"
    _try_source "$plugin_dir/$plugin_name.zsh"
    _try_source "$plugin_dir/$plugin_name.zsh-theme"
}

I don't think we even need the completion part tbh