gitignore: Add *.ttf/png and cleanup whitespace

- Ignore ttf/png assets generated by `make html`.
- Remove trailing whitespaces.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>

Author: EricccTaiwan

.gitignore

@@ -20,21 +20,23 @@ lkmpg.pdf
 *.toc
 *.bbl
 *.blg
-*.fdb_latexmk 
+*.fdb_latexmk
 *.fls
 lkmpg.synctex.gz
 
 # make4ht
 *.html
-*.svg 
+*.svg
 *.tmp
-*.css 
-*.4ct 
-*.4tc 
-*.dvi 
-*.lg 
+*.css
+*.4ct
+*.4tc
+*.dvi
+*.lg
 *.idv
 *.xref
+*.ttf
+*.png
 
 # format checks
 expected-format