New formats added to export list

[jonnybazookatone]

Noticed there was some new formats added to the export end point, so added them in the client.

[coveralls]

Coverage remained the same at 92.052% when pulling 6ccae32 on jonnybazookatone:feature/export-types-update into bd3dc5b on andycasey:master.

[vsudilov]

Could you test those live with your personal api key just to make sure nothing breaks on either our end or ads?

[jonnybazookatone]

Yeah, I did, they're fine:

In [3]: import ads

In [4]: ads.ExportQuery(bibcodes='2017NewA...52..133P', format='mnras').execute()
Out[4]: '\\bibitem[\\protect\\citeauthoryear{Paunzen et al.}{2017}]{2017NewA...52..133P} Paunzen E., et al., 2017, NewA, 52, 133 \n\n\n'

In [5]: ads.ExportQuery(bibcodes='2017NewA...52..133P', format='soph').execute()
Out[5]: "\\bibitem[Paunzen \\emph{et al.}(2017)]{2017NewA...52..133P}Paunzen, E., Handler, G., Lendl, M., Baumann, B., Rab, C., Meingast, S., Rode-Paunzen, M., Netopil, M., Antoci, V., Zhu, L., Zejda, M., and Bo{\\v z}i{\\'c}, H.: 2017, {\\it New Astronomy} {\\bf 52}, 133. \n\n\n"