wrote tests for 4.2.(3 5 6)

Test:80     Success:75     Failure:0     Error:5
add sections in README.md
tests for 6.3.3 Symbols

Test:93     Success:75     Failure:0     Error:18
implement symbol?, symbol->string, string->symbol

string->symbol converts upper case letters to lower case letters, which is not correct.
They should not be converted to other letters, so that (symbol->string (string->symbol s)) is evaluated to s itself.
string->symbol

string->symbol converts a string into a symbol correctly.
Some tests fail because of the lack of eq? and string=?
Test:93     Success:84     Failure:0     Error:9