The output module name used by protoc-gen-twirp_haskell is too restrictive

[neilmayhew]

1. The pascalCase applied to package names isn't always appropriate. I'm using a package name of Product.RPC.Service in my proto file, and I want that to be the package name of the generated API module. However, protoc-gen-twirp_haskell changes it to Product.Rpc.Service which doesn't fit with our project's naming conventions.

2. proto-lens-protoc puts its output into Proto.* regardless of the package name. I guess I should make an issue for this in proto-lens-protoc.

I'm solving (1) by specifying the output directory I want and then changing the module name in the generated source using a post-processing step after running protoc. I could do something similar for (2) but it would be more complicated so I've left it alone for now.

A possible solution for (1) would be to examine the first character of each dot-separated segment and make no changes if it's already capitalized.

I can see that there's some commented-out code for handling "API" specially, so presumably this issue has come up before.