Decodes a character string, raw vector or other object from base64 encoding.
Details
The value of convert should be set to TRUE, FALSE or NA to be the
reverse of the 3 encoding operations (for strings, raw vectors and arbitrary
objects), in order to return the original object.
References
This implementation is based that by 'The Mbed TLS Contributors' under the 'Mbed TLS' Trusted Firmware Project at https://www.trustedfirmware.org/projects/mbed-tls.