Fix style issues

Based on PullReview report.

* Space missing to the left of `{`
* Surrounding space missing for operator `/`
* Surrounding space missing in default value assignment
* 1 trailing blank lines detected
* Remove trailing whitespace
* Avoid using {} for multi line blocks
* Don't use parentheses around the condition of an `if`
* Prefer single quoted strings when you don't need string
  interpolation or special symbols
* Space between `{` and `|` missing
* Space inside parentheses detected
* Space missing after comma
* Space missing inside `}`
* Surrounding space missing in default value assignment
* Use empty lines between defs
* Add underscores to large numeric literals to improve
  their readability