Fix typos and other issues in docs

This fixes spelling, grammar and punctuation issues, missing words and
stray words across the documentation.  A confusing sentence was removed
from the tutorial.

Closes #2085

(cherry picked from commit 2e12ef00bb)

docs/moving.dox

@@ -243,7 +243,7 @@ while (!glfwWindowShouldClose(window))
 @endcode
 
 The close callback no longer returns a value.  Instead, it is called after the
-close flag has been set so it can override its value, if it chooses to, before
+close flag has been set, so it can optionally override its value, before
 event processing completes.  You may however not call @ref glfwDestroyWindow
 from the close callback (or any other window related callback).
 
@@ -350,11 +350,11 @@ from a repeat.  Note that @ref glfwGetKey still returns only `GLFW_PRESS` or
 
 GLFW 3 key tokens map to physical keys, unlike in GLFW 2 where they mapped to
 the values generated by the current keyboard layout.  The tokens are named
-according to the values they would have using the standard US layout, but this
+according to the values they would have in the standard US layout, but this
 is only a convenience, as most programmers are assumed to know that layout.
 This means that (for example) `GLFW_KEY_LEFT_BRACKET` is always a single key and
 is the same key in the same place regardless of what keyboard layouts the users
-of your program has.
+of your program have.
 
 The key input facility was never meant for text input, although using it that
 way worked slightly better in GLFW 2.  If you were using it to input text, you