Remove choose_package_with_fewest_versions (#15)

src/limitations/multiple_versions.md

@@ -157,7 +157,7 @@ index.add_deps("a", (2, 0, 0), &[("b", (1, 0, 0)..)]);
 ### Implementing a dependency provider for the index
 
 Since our `Index` is ready, we now have to implement the `DependencyProvider`
-trait for it. As explained previously, we'll need to differenciate packages
+trait for it. As explained previously, we'll need to differentiate packages
 representing buckets and proxies, so we define the following new `Package` type.
 
 ```rust
@@ -180,13 +180,15 @@ pub struct Bucket {
 }
 ```
 
-In order to implement the first required method, `choose_package_version`, we
-simply reuse the `choose_package_with_fewest_versions` helper function provided
-by pubgrub. That one requires a list of available versions for each package, so
-we have to create that list. As explained previously, listing the existing
-(virtual) versions depend on if the package is a bucket or a proxy. For a bucket
-package, we simply need to retrieve the original versions and filter out those
-outside of the bucket.
+Any `prioritize` will work equally well for this example, even just returning a
+constant value.
+
+Let's implement the second function required by a dependency provider,
+`choose_version`. For that we defined a `available_versions()` method on an
+`Index` to list existing versions of a given package in descending order. As
+explained previously, listing the existing (virtual) versions depend on if the
+package is a bucket or a proxy. For a bucket package, we simply need to retrieve
+the original versions and filter out those outside of the bucket.
 
 ```rust
 match package {

src/limitations/optional_deps.md

@@ -125,7 +125,8 @@ pub enum Package {
 }
 ```
 
-We'll ignore `prioritize` for this example.
+Any `prioritize` will work equally well for this example, even just returning a
+constant value.
 
 Let's implement the second function required by a dependency provider,
 `choose_version`. For that we defined the `base_pkg()` method on a `Package`

src/limitations/public_private.md

@@ -200,10 +200,12 @@ pub struct Seed {
 }
 ```
 
-Implementing `choose_package_version` is trivial if we simply use the function
-`choose_package_with_fewest_versions` provided by pubgrub. Implementing
-`get_dependencies` is slightly more complicated. Have a look at the complete
-implementation if needed, the main ideas are the following.
+Any `prioritize` will work equally well for this example, even just returning a
+constant value. Implementing `choose_version` is straightforward enough not to
+get additional commentary.
+
+Implementing `get_dependencies` is slightly more complicated. Have a look at the
+complete implementation if needed, the main ideas are the following.
 
 ```rust
 fn get_dependencies(&self, package: &Package, version: &SemVer)