node_spacing parameter for .text() similar to spacing, for number of pixels between nodes

[WitherredAway]

This pull request adds an additional parameter to Pilmoji.text() that lets you specify the spacing between each node. This can come in handy as illustrated by the following example:

Before

Without the node_spacing parameter, you would have no choice but to accept this ugly spacing between each node (emoji in this case) on each line. You can pass in a negative value in the spacing parameter to deal with the line spacing, but there is no way to do that for between nodes

After

With the node_spacing parameter, you can pass in a negative value to deal with the spacing between nodes, and have smooth emoji arrays!

Note: I initially renamed spacing parameter to line_spacing to properly distinguish them, but that would be a breaking change and I'm not sure how you'd feel about that so I leave that up to you if you deem fit!

[jay3332]

LGTM, thanks for the PR!