renderer fonts: additions and improvements

* Allow passing font options to renderer.font:copy().
* Added renderer.font:get_path()
* Reintroduced set_size() for more faster font size changes
* Swapped copy wiht set_size on scale plugin for better performance
* Use code_font:copy() instead of renderer.font.load() on language_md to
  properly match user font now that font options are supported on copy.
* Added new changes to renderer docs

data/plugins/language_md.lua

@@ -14,9 +14,7 @@ for _, attr in pairs({"bold", "italic", "bold_italic"}) do
     attributes["bold"] = true
     attributes["italic"] = true
   end
-  -- no way to copy user custom font with additional attributes :(
-  style.syntax_fonts["markdown_"..attr] = renderer.font.load(
-    DATADIR .. "/fonts/JetBrainsMono-Regular.ttf",
+  style.syntax_fonts["markdown_"..attr] = style.code_font:copy(
     style.code_font:get_size(),
     attributes
   )

data/plugins/scale.lua

@@ -79,14 +79,14 @@ local function set_scale(scale)
     style.tab_width      = style.tab_width      * s
 
     for _, name in ipairs {"font", "big_font", "icon_font", "icon_big_font", "code_font"} do
-      style[name] = renderer.font.copy(style[name], s * style[name]:get_size())
+      style[name]:set_size(s * style[name]:get_size())
     end
   else
-    style.code_font = renderer.font.copy(style.code_font, s * style.code_font:get_size())
+    style.code_font:set_size(s * style.code_font:get_size())
   end
 
   for name, font in pairs(style.syntax_fonts) do
-    style.syntax_fonts[name] = renderer.font.copy(font, s * font:get_size())
+    style.syntax_fonts[name]:set_size(s * font:get_size())
   end
 
   -- restore scroll positions
@@ -108,12 +108,10 @@ end
 
 local function inc_scale()
   set_scale(current_scale + scale_steps)
-  collectgarbage "step"
 end
 
 local function dec_scale()
   set_scale(current_scale - scale_steps)
-  collectgarbage "step"
 end