Keep the same tense in docstrings, and remove a little ambiguity

README

@@ -92,28 +92,28 @@ foo.Println(foo.Num)
 == Reference
 
 func New(de, ci time.Duration) *Cache
-    Returns a new cache with a given default expiration duration and cleanup
+    Return a new cache with a given default expiration duration and cleanup
     interval. If the expiration duration is less than 1, the items in the cache
     never expire (by default), and must be deleted manually. If the cleanup
     interval is less than one, expired items are not deleted from the cache
     before their next lookup or before calling DeleteExpired.
 
 func (c *Cache) Set(k string, x interface{}, d time.Duration)
-    Adds an item to the cache, replacing any existing item. If the duration is
+    Add an item to the cache, replacing any existing item. If the duration is
     0, the cache's default expiration time is used. If it is -1, the item never
     expires.
 
 func (c *Cache) Add(k string, x interface{}, d time.Duration) error
-    Adds an item to the cache only if an item doesn't already exist for the
+    Add an item to the cache only if an item doesn't already exist for the
     given key, or if the existing item has expired. Returns an error if not.
 
 func (c *Cache) Replace(k string, x interface{}, d time.Duration) error
-    Sets a new value for the cache item only if it already exists. Returns an
+    Set a new value for the cache key only if it already exists. Returns an
     error if it does not.
 
 func (c *Cache) Get(k string) (interface{}, bool)
-    Gets an item from the cache. Returns the item or nil, and a bool indicating
-    whether the given key was found in the cache.
+    Get an item from the cache. Returns the item or nil, and a bool indicating
+    whether the key was found.
 
 func (c *Cache) Increment(k string, n int64) error
     Increment an item of type int, int8, int16, int32, int64, uintptr, uint,
@@ -136,28 +136,28 @@ func (c *Cache) Decrement(k string, n int64) error
     possible to decrement it by n.
 
 func (c *Cache) Delete(k string)
-    Deletes an item from the cache. Does nothing if the item does not exist in
-    the cache.
+    Delete an item from the cache. Does nothing if the key does not exist in the
+    cache.
 
 func (c *Cache) DeleteExpired()
-    Deletes all expired items from the cache.
+    Delete all expired items from the cache.
 
 func (c *Cache) Flush()
-    Deletes all items from the cache.
+    Delete all items from the cache.
 
 func (c *Cache) Save(w io.Writer) error
-    Writes the cache's items (using Gob) to an io.Writer. Returns an error if
+    Write the cache's items (using Gob) to an io.Writer. Returns an error if
     the serialization fails, e.g. because there are unserializable objects like
     channels in the cache.
 
 func (c *Cache) SaveFile(fname string) error
-    Saves the cache's items to the given filename, creating the file if it
+    Save the cache's items to the given filename, creating the file if it
     doesn't exist, and overwriting it if it does.
 
 func (c *Cache) Load(r io.Reader) error
-    Adds (Gob-serialized) cache items from an io.Reader, excluding any items
-    that already exist in the current cache.
+    Add (Gob-serialized) cache items from an io.Reader, excluding any items
+    with keys that already exist in the current cache.
 
 func (c *Cache) LoadFile(fname string) error
     Loads and adds cache items from the given filename, excluding any items
-    that already exist in the current cache.
+    with keys that already exist in the current cache.