Fix problems with rmWhitespace

[nwoltman]

Make rmWhitespace safer by handling empty lines better and not removing newlines around EJS tags.

Fixes #406

Example

<h2>
  <%- 'EJS' %>
  Title
</h2>
<div>
  <span>1</span>
  <span>2</span>

  <span>3</span>
</div>

Before:

<h2>
EJSTitle
</h2>
<div>
<span>1</span>
<span>2</span><span>3</span>
</div>

After:

<h2>
EJS
Title
</h2>
<div>
<span>1</span>
<span>2</span>
<span>3</span>
</div>

[mde]

LGTM. Thanks so much for this!