add acs template

add plos one namespace and revise yaml
Right now the acs(American Chemistry Society) template is more like a tex document than markdown document. 
There are two issues:
- the email in the yaml can't be  a link. I tried to add the herperref package in the template but the document can't be complied
- the author can't be more than one, I think this issue due to the conflict between the yaml grammar and some wired definitions in the achemso package
- achemso package defined many environments while markdown were not support that, so I just write plain tex in the template
I think you mean `keep_tex = keep_tex` here.