ELF information in specdb incomplete

The information about the ELF file format captured in the database is
not complete; where the specification has information on missing pieces
it is either hand-written, or included by reference (e.g., may be described
in "ABI Update").

The example which causes me to file this bug (there may be others) is
that there is not information on the program header, which contains
descriptions of Segments and their types (PT_DYNAMIC,
PT_SHLIB, PT_TLS, etc.) These Segments then contain Sections, and we
do have descriptions of the Sections. This is the material which appears
in first part of Chapter 5 of the gABI / ABI Update under Program Header.

This kind of information on the elf file structure is hardcoded into the
elfchk code, so it works there, but as it's not in the database we're not
able to pull any information on this out of Navigator, and in a sense,
Navigator misrepresents the structure of ELF as a result,

It may not be crucial to address this, just thought it ought to be
recorded somewhere.