enforce naming convention for non-exported members

Rename all private structs, enums, non-static functions, and global
variables to include a leading '_alpm'.  Doxygen will pick up these
members by default.  Enforcing a common naming convention for these
members allows them to all be easily excluded from our public
documentation and puts them in our actual namespace.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
rename doxygen groups

Prefix groups with 'libalpm' and remove '_api'.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
set doxygen groups in header files

Managing member grouping is much more easily done within header files
where we have all of the members together in one place.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
remove libalpm.3.txt

Replaced by doxygen-generated manpage.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>