Add interface for working with BookmarkCollection

Oh my god I'm so drunk right now.
It's 0030 and I had dinner at around 1800 yesterday and then I just
drank like... two Mate and maybe 1L of water... and now I drank 0.33L
beer and I'm drunk as fuck... just wanted to share.

I hope this commit still makes sense... I'm not sure, I should
definitively review this tomorrow.

So... maybe I can do some more.

Btw., I just saw "The Martian" - the movie, you know. Oh my god, I love
Matt Damon - I think he's a really nice actor, actually.

I probably shouldn't put this into the commit message, I know... Just
wanted to have some fun here.. sorry.

libimagbookmark/src/collection.rs

@@ -18,10 +18,12 @@ use libimagstore::storeid::IntoStoreId;
 use libimagstore::store::FileLockEntry;
 use libimagentrylink::external::ExternalLinker;
 use libimagentrylink::internal::InternalLinker;
-use libimagentrylink::internal::Link;
+use libimagentrylink::internal::Link as StoreLink;
 use libimagerror::into::IntoError;
 use url::Url;
 
+use link::Link;
+
 pub struct BookmarkCollection<'a> {
     fle: FileLockEntry<'a>,
     store: &'a Store,
@@ -82,7 +84,7 @@ impl<'a> BookmarkCollection<'a> {
         self.fle.get_external_links(&self.store).map_err_into(BEK::LinkError)
     }
 
-    pub fn link_entries(&self) -> Result<Vec<Link>> {
+    pub fn link_entries(&self) -> Result<Vec<StoreLink>> {
         use libimagentrylink::external::is_external_link_storeid;
 
         self.fle
@@ -91,5 +93,21 @@ impl<'a> BookmarkCollection<'a> {
             .map_err_into(BEK::StoreReadError)
     }
 
+    pub fn add_link(&self, l: Link) -> Result<()> {
+        unimplemented!()
+    }
+
+    pub fn get_link(&self, l: Link) -> Result<Link> {
+        unimplemented!()
+    }
+
+    pub fn get_links_matching(&self, r: Regex) -> Result<Link> {
+        unimplemented!()
+    }
+
+    pub fn remove_link(&self, l: Link) -> Result<()> {
+        unimplemented!()
+    }
+
 }