Support nested partitions and partitions directly targeting services (#122)

* Do the nested partition thing

* Tidy up touched code

* Add nested partition test project, not fully functional

* Clean up variable names, move path_metadata mutation strictly into snapshot_reconciler

* Remove path_metadata, snapshotting is now pure

* Factor out snapshot metadata storage to fix a missing case

* Pull instance_name out of per_path_metadata, closer to what we need

* Refactor to make metadata make more sense, part one

* All appears to be well

* Cull 'metadata_per_path' in favor of 'instances_per_path'

* Remove SnapshotContext

* InstanceMetadata -> PublicInstanceMetadata in web module

* Build in snapshot testing system for testing... snapshots?

* Remove pretty_assertions to see if it fixes a snapshot comparison bug

* Reintroduce pretty assertions, it's not the cause of inequality

* Fix snapshot tests with custom relative path serializer

server/src/path_map.rs

@@ -1,5 +1,4 @@
 use std::{
-    collections::hash_map,
     path::{self, Path, PathBuf},
     collections::{HashMap, HashSet},
 };
@@ -36,12 +35,6 @@ impl<T> PathMap<T> {
         self.nodes.get_mut(path).map(|v| &mut v.value)
     }
 
-    pub fn entry<'a>(&'a mut self, path: PathBuf) -> Entry<'a, T> {
-        Entry {
-            internal: self.nodes.entry(path),
-        }
-    }
-
     pub fn insert(&mut self, path: PathBuf, value: T) {
         if let Some(parent_path) = path.parent() {
             if let Some(parent) = self.nodes.get_mut(parent_path) {
@@ -116,28 +109,4 @@ impl<T> PathMap<T> {
 
         current_path
     }
-}
-
-pub struct Entry<'a, T> {
-    internal: hash_map::Entry<'a, PathBuf, PathMapNode<T>>,
-}
-
-impl<'a, T> Entry<'a, T> {
-    pub fn or_insert(self, value: T) -> &'a mut T {
-        &mut self.internal.or_insert(PathMapNode {
-            value,
-            children: HashSet::new(),
-        }).value
-    }
-}
-
-impl<'a, T> Entry<'a, T>
-    where T: Default
-{
-    pub fn or_default(self) -> &'a mut T {
-        &mut self.internal.or_insert(PathMapNode {
-            value: Default::default(),
-            children: HashSet::new(),
-        }).value
-    }
 }