Fix epub build and remove redudant mkdir calls

1) ebook was still using the old target
2) Do not call mkdir -p for every single image conversion

Author: cedounet

book/makefile

@@ -83,7 +83,7 @@ website_dir := static_website_html
 website_assets := $(wildcard ../website/assets/*)
 ruby_src := ../website/modify_build.rb $(website_assets)
 ruby_pkg := ../website/Gemfile ../website/Gemfile.lock
-#}}}
+# }}}
 
 # Internal build rules {{{
 # Flowcharts {{{
@@ -118,7 +118,7 @@ book_sans_serif/book_sans_serif.pdf: $(src_all)
 epub/%.epub: %.tex $(ebook_src) cover/cover-page.xbb
 	$(EBOOK) $<
 
-copy_ebook_files: build_ebook
+copy_ebook_files: ebook
 	$(RSYNC) --exclude '*.png' epub_build/book-epub/ bw-book-epub/
 
 # Now that we have built the ebook we will generate 2 more versions
@@ -130,30 +130,33 @@ copy_ebook_files: build_ebook
 
 # We do not convert SVG to B&W or lower res for now as they are super small
 # anyway
-bw-book-epub/OEBPS/%.jpg: %.jpg
-	mkdir -p $(dir $@)
+bw-book-epub-dir:
+	mkdir -p bw-book-epub/OEBPS
+
+bw-book-epub/OEBPS/%.jpg: %.jpg | bw-book-epub-dir
 	$(CONVERT_PIC) $< $(REDUCE_PIC) $@
 
-bw-book-epub/OEBPS/%.png: %.png
-	mkdir -p $(dir $@)
+bw-book-epub/OEBPS/%.png: %.png  | bw-book-epub-dir
 	$(CONVERT_PIC) $< $(REDUCE_PIC) $@
 
 epub/bw_book.epub: copy_ebook_files $(bw_images)
 	cd bw-book-epub; zip -q0X ../epub/bw_book.epub mimetype
 	cd bw-book-epub; zip -q9XrD ../epub/bw_book.epub ./
 
-# Now the low res
+# Now the low res | low-res-book-epub-dir
+low-res-book-epub-dir:
+	mkdir -p low-res-book-epub/OEBPS
+
 copy_ebook_files_low_res: ebook
 	$(RSYNC) epub_build/book-epub/ low-res-book-epub/
 
-low-res-book-epub/OEBPS/%.jpg: %.jpg
-	mkdir -p $(dir $@)
+low-res-book-epub/OEBPS/%.jpg: %.jpg | low-res-book-epub-dir
 	$(CONVERT_PIC) $< $(REDUCE_PIC_COLOR) $@
 
 epub/low_res_book.epub: copy_ebook_files_low_res $(low_res_images)
 	cd low-res-book-epub; zip -q0X ../epub/low_res_book.epub mimetype
 	cd low-res-book-epub; zip -q9XrD ../epub/low_res_book.epub ./
-#}}}
+# }}}
 
 # Website {{{
 ###################################