Rework Safe Module (#83)

* Initial fork on minimal safe submodule

* Add new Safe module

Signed-off-by: Stephen Diehl <stephen.m.diehl@gmail.com>

* Refactor Safe module

protolude.cabal

@@ -7,7 +7,7 @@ license:             MIT
 license-file:        LICENSE
 author:              Stephen Diehl
 maintainer:          stephen.m.diehl@gmail.com
-copyright:           2016-2017 Stephen Diehl
+copyright:           2016-2018 Stephen Diehl
 category:            Prelude
 build-type:          Simple
 cabal-version:       >=1.10
@@ -51,6 +51,7 @@ library
     Protolude.CallStack
     Protolude.Error
     Protolude.Panic
+    Protolude.Safe
 
   default-extensions:
     NoImplicitPrelude
@@ -78,12 +79,5 @@ library
     mtl-compat          >= 0.2  && <0.3,
     transformers-compat >= 0.4  && <0.7
 
-  if impl(ghc >= 7.8.0)
-    build-depends:
-      safe             >= 0.3  && <0.4
-  else
-    build-depends:
-      safe             >= 0.3  && <0.3.10
-
   hs-source-dirs:      src
   default-language:    Haskell2010