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.
