Whitespace corrections to CMakeLists.txt;
tests/CMakeLists.txt:
  -missing library in link command, and link order:
    -Corrected link command for stream_output_checks;
    -Corrected link command for multiple_errors_checks;
Adding additional test source code;
  tests/multiple_errors_checks.cpp
  tests/stream_output_checks.cpp
Forward declerations of functions moved to header file;

inc/symmetric_error.hpp:
  Added includes for <vector> and <tuple>;
  Added forward declarations of functions:
    to_tuple_multi_errors
    value_to_string_multiple_errors
    to_string_multiple_errors_into_vector
    to_string_no_exponent
    to_string_no_exponent
    to_string_no_exponent
    to_string_no_exponent

src/symmetric_error.cpp
  Removed #include <tuple> [now in header]
Replace explicit template parameter;
  to_fixed_string<double> -> to_fixed_string