Prefer short symbol key syntax over hash rockets

It makes the code cleaner and easier to read.
Update examples to obey rule for percent literals

Update examples using parentheses (`()`) to use square brackets (`[]`)
in order to not break rule "Prefer `[]` as delimiters for all `%`
literals".
Do not recommend to rely on hashes being ordered

Although an ordered hash can come in useful at times, hashes in general
are often thought of as begin unordered. An implementation that relies
on the fact that a hash retains the order of its keys can therefore
possibly be a source of confusion. We should not explicitly recommend
it. Let developer use brain and decide case by case.
Update string interpolation examples to obey rule

Update examples so that they do not break the rule "Use `{}` around
instance variables being interpolated into a string".
Fix formatting and typo
Align variable with opening quote instead of string content

Although aesthetically it may look better to align a variable with the
content of an adjacent string instead of its opening quote, the variable
substitutes what would otherwise be a full quoted string and should so
be aligned accordingly.
Update example for usage of {} for string interpolation

Example and text did not agree.
Merge pull request #2 from jsageryd/johan

Johan