alias touhou_project -> touhou

BUR #4177 has been rejected.

create alias touhou_project -> touhou

The idea of renaming Touhou to Touhou Project has been unilaterally rejected (topic #16920), but the name "Touhou Project" is common enough that it should be in the system as an alias.

I don't see much point in an alias that's longer than the original tag while sharing the same first word.

The bulk update request #4177 (forum #177339) has been rejected by @Hillside_Moose.