update AUTHORS and ChangeLog
readme: library -> C library
Ignore .dirstamp files

The autotools build system now produces .dirstamp files.

Signed-off-by: Sebastian Ramacher <sramacher@debian.org>
Merge remote-tracking branch 'sebastinas/gitignore-dirstamp'

see pull-request #18
mention available feature matrix
remove read_sparse contradiction in the docs

Since DISCID_FEATURE_READ == 0, you automatically specify this feature.
So we should explicitely say, that read_sparse always reads the TOC.

For the same reason we can't and we don't have to test
if the feature is requested in the code.
`features & 0` is always `0`.

Note that `has_feature(DISCID_FEATURE_READ)` doesn't work with bit masks,
but is implemented with switch.
state that has_feature doesn't take bit masks

The signature is fine (enum discid_feature),
but people still might think they can use a "full-blown" integer
that is evaluated as bit mask.
DISCID_FEATURE_READ == 1, not 0

Thanks Sebastinas for catching that.
Doesn't make a difference in how it works, but it is a bit less
transparent.