oughta: Rename from FileCheck

[langston-barrett]

Fixes #96.

[RyanGlScott]

There are some lingering filecheck references that ought to be updated as well:

• grease/oughta/src/Oughta/LuaApi.hs

  Line 159 in 4fbbb9f

  _ <- Lua.loadbuffer FCL.luaCode (Lua.Name "filecheck.lua")

• grease/oughta/src/Oughta/Exception.hs

  Line 35 in 4fbbb9f

  show (NoMatch {}) = "filecheck: no match"

• grease/doc/dev.md

  Line 71 in 4fbbb9f

  hlint grease{,-aarch32,-ppc,-x86}/src grease-cli/{main,src,tests} filecheck/{src,test}