title: "Your requirements could not be resolved to an installable set of packages" when installing laravel 5 simple-blog
body: <p>When I type "composer create-project laravel/laravel simple-blog" to load simple-blog from the server, I receive an error: </p>
  
  <pre><code>Loading composer repositories with package information
  Installing dependencies (including require-dev)
  Your requirements could not be resolved to an installable set of packages.
  
  Problem 1
  - laravel/framework v5.2.6 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.5 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.4 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.3 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.2 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.1 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - laravel/framework v5.2.0 requires ext-mbstring * -&gt; the requested PHP extension mbstring is missing from your system.
  - Installation request for laravel/framework 5.2.* -&gt; satisfiable by laravel/framework[v5.2.0, v5.2.1, v5.2.2, v5.2.3, v5.2.4, v5.2.5, v5.2.6].
  </code></pre>
  
  <p>Can anyone tell me what is going wrong?</p>