Replace string concatenation

[bastisawesome]

Currently some of the codebase uses the string concatenation operator, which creates string copies and unnecessary memory and CPU usage. Replace string concatenation, where possible, with io.StringIO instead.

[bastisawesome]

Before working on this, might be best to benchmark the two possible solutions and see which one produces consistently better results, or even if there's a non-negligible difference.

Testing should be relatively simple:

• Copy the logic used by the repo into a test file
• Duplicate and replace with StringIO logic
• Run both methods a few hundred times to get an average score, possibly collecting other metrics
• Profit!

This may turn out to be premature optimisation and, if it's even worthwhile, might be pushed back to a later release, unless someone else wants to take over and submit a PR. If the metrics don't seem to impact performance in any meaningful way, this may just be scrapped.

[bastisawesome]

Moving this out of the 1.1.0 release. Reason: this assumes a performance penalty that may be a micro-optimisation. A much better solution would be to actually profile the code and see if this is a worthwhile endeavour. Issue will remain open just in case.