Add case protection for postgreSQL

[kilnerm]

Add case protection for names.

• Updated SwiftKuery tests to check all identifiers are wrapped in "'s. (apart from raw strings)
• Updated build functions to wrap identifiers when building SQL statements.

Mixed case column names now work consistently across postgreSQL, mySQL and SQLite.

[codecov-io]

Codecov Report

Merging #130 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #130      +/-   ##
==========================================
+ Coverage   84.55%   84.58%   +0.02%     
==========================================
  Files          43       43              
  Lines        3606     3606              
==========================================
+ Hits         3049     3050       +1     
+ Misses        557      556       -1

Flag	Coverage Δ
#SwiftKuery	84.58% <100%> (+0.02%)	⬆️

Impacted Files	Coverage Δ
Sources/SwiftKuery/Utils.swift	56% <100%> (+1.33%)	⬆️
Sources/SwiftKuery/RawField.swift	100% <100%> (ø)	⬆️
Sources/SwiftKuery/Insert.swift	97.53% <100%> (ø)	⬆️
Sources/SwiftKuery/Select.swift	86.53% <100%> (ø)	⬆️
Sources/SwiftKuery/Column.swift	90.16% <100%> (ø)	⬆️

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[EnriqueL8]

This would be a BREAKING CHANGE.