Make links detect target automatically and replace false with null for no attribute

New version of Harp would render attribute=false as attribute="false",
while attribute=null renders element without attribute.

website/_includes/_footer.jade

@@ -11,7 +11,7 @@ footer.o-footer.u-text.u-border-dotted
 
                     each url, item in group
                         li
-                            +a(url)(target=url.includes("http") ? "_blank" : false)=item
+                            +a(url)=item
 
         if SECTION != "docs"
             +grid-col("quarter")

website/_includes/_mixins.jade

@@ -20,7 +20,8 @@ mixin h(level, id)
               info: https://mathiasbynens.github.io/rel-noopener/
 
 mixin a(url, trusted)
-    a(href=url target="_blank" rel=!trusted ? "noopener nofollow" : false)&attributes(attributes)
+    - external = url.includes("http")
+    a(href=url target=external ? "_blank" : null rel=external && !trusted ? "noopener nofollow" : null)&attributes(attributes)
         block
 
 
@@ -74,7 +75,8 @@ mixin aside-code(label, language)
                see assets/css/_components/_buttons.sass
 
 mixin button(url, trusted, ...style)
-    a.c-button.u-text-label(href=url class=prefixArgs(style, "c-button") role="button" target="_blank" rel=!trusted ? "noopener nofollow" : false)&attributes(attributes)
+    - external = url.includes("http")
+    a.c-button.u-text-label(href=url class=prefixArgs(style, "c-button") role="button" target=external ? "_blank" : null rel=external && !trusted ? "noopener nofollow" : null)&attributes(attributes)
         block
 
 
@@ -148,7 +150,7 @@ mixin tag()
 
 mixin list(type, start)
     if type
-        ol.c-list.o-block.u-text(class="c-list--#{type}" style=(start === 0 || start) ? "counter-reset: li #{(start - 1)}" : false)&attributes(attributes)
+        ol.c-list.o-block.u-text(class="c-list--#{type}" style=(start === 0 || start) ? "counter-reset: li #{(start - 1)}" : null)&attributes(attributes)
             block
 
     else

website/_includes/_navigation.jade

@@ -2,7 +2,7 @@
 
 include _mixins
 
-nav.c-nav.u-text.js-nav(class=landing ? "c-nav--theme" : false)
+nav.c-nav.u-text.js-nav(class=landing ? "c-nav--theme" : null)
     a(href='/') #[+logo]
 
     if SUBSECTION != "index"
@@ -11,7 +11,7 @@ nav.c-nav.u-text.js-nav(class=landing ? "c-nav--theme" : false)
     ul.c-nav__menu
         each url, item in NAVIGATION
             li.c-nav__menu__item
-                a(href=url target=url.includes("http") ? "_blank" : false)=item
+                +a(url)=item
 
         li.c-nav__menu__item
             +a(gh("spaCy"))(aria-label="GitHub").u-hidden-xs #[+icon("github", 20)]

website/_includes/_sidebar.jade

@@ -9,5 +9,5 @@ menu.c-sidebar.js-sidebar.u-text
                 li.u-text-label.u-color-subtle=menu
 
                 each url, item in items
-                    li(class=(CURRENT == url || (CURRENT == "index" && url == "./")) ? "is-active" : false)
-                        +a(url)(target=url.includes("http") ? "_blank" : false)=item
+                    li(class=(CURRENT == url || (CURRENT == "index" && url == "./")) ? "is-active" : null)
+                        +a(url)=item

website/index.jade

@@ -22,7 +22,7 @@ include _includes/_mixins
                 |  process entire web dumps, spaCy is the library you want to
                 |  be using.
 
-            +button("/docs/api", true, "primary")(target="_self")
+            +button("/docs/api", true, "primary")
                 |  Facts & figures
 
         +grid-col("third").o-card
@@ -35,7 +35,7 @@ include _includes/_mixins
                 |  think of spaCy as the Ruby on Rails of Natural Language
                 |  Processing.
 
-            +button("/docs/usage", true, "primary")(target="_self")
+            +button("/docs/usage", true, "primary")
                 |  Get started
 
         +grid-col("third").o-card
@@ -51,7 +51,7 @@ include _includes/_mixins
                 |  connect the statistical models trained by these libraries
                 |  to the rest of your application.
 
-            +button("/docs/usage/deep-learning", true, "primary")(target="_self")
+            +button("/docs/usage/deep-learning", true, "primary")
                 |  Read more
 
 .o-inline-list.o-block.u-border-bottom.u-text-small.u-text-center.u-padding-small
@@ -105,7 +105,7 @@ include _includes/_mixins
                 +item Robust, rigorously evaluated accuracy
 
             .o-inline-list
-                +button("/docs/usage/lightning-tour", true, "secondary")(target="_self")
+                +button("/docs/usage/lightning-tour", true, "secondary")
                     | See examples
 
     .o-block.u-text-center.u-padding