title: Format a number to always have a sign and decimal separator
body: <p>I want to format any number (integer or real) to a string representation which <strong>always</strong> has <strong>a sign</strong> (positive or negative) and a <strong>decimal separator</strong>, but no trailing zeroes.</p>
  
  <p>Some samples:</p>
  
  <pre><code>3.14 =&gt; +3.14
  12.00 =&gt; +12.
  -78.4 =&gt; -78.4
  -3.00 =&gt; -3.
  </code></pre>
  
  <p>Is it possible with one of the default <code>ToString()</code> implementations, or do I need write this myself?</p>