Move doctests to shell script

This fixes various problems with doctest:

* https://github.com/sol/doctest/issues/245
* https://github.com/composewell/streamly/issues/83

Also clean up travis.yml for cabal-3.

hpath.cabal

@@ -13,8 +13,6 @@ cabal-version:       1.14
 extra-source-files:  README.md
                      CHANGELOG
                      cbits/dirutils.h
-                     doctests-hpath.hs
-                     doctests-posix.hs
 
 library
   if os(windows)
@@ -41,7 +39,6 @@ library
                    , deepseq
                    , exceptions
                    , hspec
-                   , simple-sendfile >= 0.2.24
                    , streamly >= 0.7
                    , unix >= 2.5
                    , unix-bytestring
@@ -49,37 +46,6 @@ library
                    , word8
 
 
-test-suite doctests-hpath
-  if os(windows)
-    build-depends: unbuildable<0
-    buildable: False
-  default-language:  Haskell2010
-  type:              exitcode-stdio-1.0
-  ghc-options:       -threaded
-  main-is:           doctests-hpath.hs
-  build-depends:     base
-                   , HUnit
-                   , QuickCheck
-                   , doctest >= 0.8
-                   , hpath
-
-test-suite doctests-posix
-  if os(windows)
-    build-depends: unbuildable<0
-    buildable: False
-  default-language:  Haskell2010
-  type:              exitcode-stdio-1.0
-  ghc-options:       -threaded
-  main-is:           doctests-posix.hs
-  build-depends:     base,
-                     bytestring >= 0.10.0.0,
-                     unix,
-                     hpath,
-                     doctest >= 0.8,
-                     HUnit,
-                     QuickCheck,
-                     word8
-
 test-suite spec
   if os(windows)
     build-depends: unbuildable<0