Add config as language file

This patch will change several behaviour while generating the ebook:

- `build.go` now accepts two environment variables: TMP, WORKDIR

    * TMP:

Temporary directory path.
The directory stores intermediate files like '*.html' or metadata.txt.

    * WORKDIR:

Script base directory.

- `config` as language file

config file will be `source`d to change its ebook metadata.

- `genepub.sh` is integrated to `build.sh` and `build.go`

See `FixHeader` and `RemoveFooterLink` functions.

ebook/build.sh

@@ -1,11 +1,46 @@
 #!/bin/sh
 
-rm -f *.html *~
+bn="`basename $0`"
+WORKDIR="$(cd $(dirname $0); pwd -P)"
 
-export GOPATH=`pwd`
+#
+# Default language: zh
+# You can overwrite following variables in config file.
+#
+MSG_INSTALL_PANDOC_FIRST='请先安装pandoc，然后再次运行'
+MSG_SUCCESSFULLY_GENERATED='build-web-application-with-golang.epub 已经建立'
+MSG_CREATOR='Astaxie'
+MSG_DESCRIPTION='一本开源的Go Web编程书籍'
+MSG_LANGUAGE='zh-CN'
+MSG_TITLE='Go Web编程'
+[ -e "$WORKDIR/config" ] && . "$WORKDIR/config"
 
-#go get -u github.com/russross/blackfriday
+
+TMP=`mktemp -d 2>/dev/null || mktemp -d -t "${bn}"` || exit 1
+trap 'rm -rf "$TMP"' 0 1 2 3 15
+
+
+cd "$TMP"
+
+(
+[ go list github.com/fairlyblank/md2min >/dev/null 2>&1 ] || export GOPATH="$PWD"
 go get -u github.com/fairlyblank/md2min
+WORKDIR="$WORKDIR" TMP="$TMP" go run "$WORKDIR/build.go"
+)
 
-go run build.go
+if [ ! type -P pandoc >/dev/null 2>&1 ]; then
+	echo "$MSG_INSTALL_PANDOC_FIRST"
+	exit 0
+fi
 
+cat <<__METADATA__ > metadata.txt
+<dc:creator>$MSG_CREATOR</dc:creator>
+<dc:description>$MSG_DESCRIPTION</dc:description>
+<dc:language>$MSG_LANGUAGE</dc:language>
+<dc:rights>Creative Commons</dc:rights>
+<dc:title>$MSG_TITLE</dc:title>
+__METADATA__
+
+pandoc --reference-links -S --toc -f html -t epub --epub-metadata=metadata.txt --epub-cover-image="$WORKDIR/../images/cover.png" -o "$WORKDIR/../build-web-application-with-golang.epub" `ls [0-9]*.html | sort`
+
+echo "$MSG_SUCCESSFULLY_GENERATED"