doc: Add asciidoc.conf and sysdb-description.txt to EXTRA_DIST.
store_lookup: Added a matcher matching by object name.

This is a generic matcher applied to hosts (or their services or attributes)
and matches based on the respective object name.

Subsequently, this will replace the more complex host/service/attribute
matchers. Instead, more basic matchers will be available which can then be
combined arbitrarily using the existing logical matchers.
store_lookup: Let parse_cmp() use the new name matcher.
store_lookup: Removed the (now unused) service matcher.
store_lookup: Made the attribute matcher a "standalone" matcher.

The attribute matcher will now be applied to host objects directly and then
match against that host's attributes. This further simplifies parse_cmp() and
the general workflow for matchers.
store_lookup: Let attribute matchers check the attribute name.
store_lookup: Removed the (now unused) host matcher.
Cleaned up some internal type names.
store_lookup: Removed unneeded forward declarations.

Also, reshuffled some functions a bit to have a more natural order now that
the matcher approach is greatly simplified.
store: Removed a obsolete (and now somewhat misleading) comment.
store_lookup: Simplified some internal checks.
store: Don't allow name to be NULL when matching attributes.

There's no real use-case for it imho and it's just a weird special case in the
code.
store_lookup_test: Verify that NULL is not a valid attribute name.
store: Added helper function to retrieve a host's attribute.

This also fixes a memory leak in case of an data_format() error.
data: Pass 'const' data objects to strlen()/format().
store_lookup: Introduce conditional based attribute matchers.

This allows using less-than, less-equal, equal, greater-equal, greater-than
operators on attributes.