Consecutive em tags end up in __

[schtibe]

When there is a closing em tag followed by an opening one, the output will result in a double underscore, which seems to be invalid Markdown syntax. I think the _ must always be surrounded by a space in markdown.

See following test code:

from html2text import html2text

foo = """
<em>Something emphasized</em><em>followed by something else</em>
"""

print(html2text(foo))

Tested with:

• html2text 2016.9.19
• Python 3.5.3

[jonathan-s]

PR #177 should fix this.