HPCC-9090 Add base 64 encode/decode functions to the ecllibrary

This new feature contains these implementations:

1. Add wrapper functions rtlBase64Encode() and rtlBase64Decode() into eclrtl
   (.hpp and .cpp) to call Base 64 encode/decode functions (already
   implemented in jutil.cpp).
   rtlBase64Decode() has extra boolean input parameter to control error
   handling in a particular case when input string  contains '\0' char.
   Default value is false means if the input string bad then the function
   returns an empty data.
   It its value is true and exception generated.

2. Add implementation to rtlMalloc() and rtlRealloc() functions to handle
   memory allocation fault. Added macros to handle logging exact filename
   and line number if memory allocate fails.

3. Add external references and exports for functions implemented in 1. into
   Str.ecl.

4. Add test code TestBase64Codec.ecl into ecllibrary/teststd/str/ directory.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>