Added a test class for StringBuilder
Added a test that appends an empty string
Added a test that append a normal string
Added a test that appends special chars
Added a test that appends 2 string
Added a test that appends a string longer that the capacity of the builder
Added a test class for StringBuilder.appendEscaped()
Added a test with special chars
Added a test with a NULL string
Added a test with a NULL string
Minor simplifications
Moved floating point formatting to StringBuilder
Delete empty file
Moved writeTo to JsonObjectBase