XML is slow to parse and strings inside the document cannot be
memory mapped as they do not have a trailing NUL char. The libxmlb
library takes XML source, and converts it to a structured binary
representation with a deduplicated string table -- where the
strings have the NULs included.

This allows an application to mmap the binary XML file, do an XPath
query and return some strings without actually parsing the entire
document. This is all done using (almost) zero allocations and no
actual copying of the binary data.