Added Support for Line Breaks in Inline Elements

[jrg94]

Most markdown parsers support a line break feature as follows:

This line is separate from the following line  
This line is on its own line

As long as there are two spaces following the end of the first line, these two lines will render separately as follows:

This line is separate from the following line
This line is on its own line

The way this works is that markdown parsers will see the two spaces and interpret it as a line break. Therefore, the two spaces will be replaced with a line break tag (i.e., <br>).

To replicate this behavior in SnakeMD, I have added a line break feature to the Inline element. When the line break flag is True, a line break will be added at the end of the Inline element.

However, because the Paragraph element in SnakeMD removes all whitespace, we can't replicate the line break behavior exactly. As a result, rather than changing the behavior of the Paragraph element (given its potential widespread use), an HTML line break will be produced instead of two spaces.

I believe this falls in line with the expectations of this library anyway. After all, if the user wants to use markdown, there Raw element should allow them to do so.