chore: docs proofreading (#883)

docs/node/nodedb.md

@@ -109,7 +109,7 @@ func (ndb *nodeDB) deleteVersion(version int64) error {
 }
 ```
 
-##### Travesing Orphans
+##### Traversing Orphans
 
 The traverseOrphans algorithm is shown below:
 

docs/proof/proof.md

@@ -73,9 +73,9 @@ proof can prove that the key `ab` is not in the tree, because if it was it would
 ordered between `a` and `b` - it is clear from the proof that there is no such node, and if
 there was it would cause the parent hashes to be different from what we see.
 
-Range proofs can be generated for non-existant endpoints by including the nearest neighboring
+Range proofs can be generated for non-existent endpoints by including the nearest neighboring
 keys, which allows them to cover any arbitrary key range. This can also be used to generate an
-absence proof for a _single_ non-existant key, by returning a range proof between the two nearest
+absence proof for a _single_ non-existent key, by returning a range proof between the two nearest
 neighbors. The range proof is therefore a complete proof for all existing and all absent key/value
 pairs ordered between two arbitrary endpoints.
 
@@ -139,7 +139,7 @@ func main() {
 
 ### Tree Root Hash
 
-Proofs are verified against the root hash of an IAVL tree. This root hash is retrived via
+Proofs are verified against the root hash of an IAVL tree. This root hash is retrieved via
 `MutableTree.Hash()` or `ImmutableTree.Hash()`, returning a `[]byte` hash. It is also returned by 
 `MutableTree.SaveVersion()`, as shown above.
 
@@ -297,7 +297,7 @@ type RangeProof struct {
   `c=3` already traversed in `LeftPath`, and `[e]` contains data about the `e` inner node needed
   to prove `d=4`.
 
-* `Leaves` contains data about the leaf nodes in the range. For the range `a` to `e` (exluding 
+* `Leaves` contains data about the leaf nodes in the range. For the range `a` to `e` (excluding 
   `e=5`) this contains info about `a=1`, `b=2`, `c=3`, and `d=4` in left-to-right order.
 
 Note that `Leaves` may contain additional leaf nodes outside the requested range, for example to

docs/tree/mutable_tree.md

@@ -121,7 +121,7 @@ If `removeKey` does not exist in the IAVL tree, RemovedValue is `nil`.
 
 Anytime a node is unbalanced such that the height of its left branch and the height of its right branch differs by more than 1, the IAVL tree will rebalance itself.
 
-This is acheived by rotating the subtrees until there is no more than one height difference between two branches of any subtree in the IAVL.
+This is achieved by rotating the subtrees until there is no more than one height difference between two branches of any subtree in the IAVL.
 
 Since Balance is mutating the structure of the tree, any displaced nodes will be orphaned.
 
@@ -262,7 +262,7 @@ Orphaned: 6, 8
 Orphaned: 6
 ```
 
-Note: 6 got orphaned again, so omit list repitition
+Note: 6 got orphaned again, so omit list repetition
 
 #### Right Right Case