Strict setting controls \newline display-mode behavior; fix MacroExpander space handling (#1314)

* Strict setting controls \newline display-mode behavior

* Bug-fix space handling in macros

Whitespace after a \controlWord is now handled within the lexer, not by the
MacroExpander.  This way, \\ expanding to \newline doesn't accidentally
cause spaces to get consumed.

* Rename nonstrict -> reportNonstrict; strictBehavior -> useStrictBehavior

* Second category of errorCodes

src/katex.less

@@ -30,11 +30,6 @@
 
         > .katex-html {
             display: inline-block;
-
-            /* \newline doesn't do anything in display mode */
-            > .newline {
-                display: none;
-            }
         }
     }
 }
@@ -66,7 +61,7 @@
     }
 
     .katex-html {
-        /* \newline is an empty block at top level of inline mode */
+        /* \newline is an empty block at top level, between .base elements */
         > .newline {
             display: block;
         }