Turn the GF compiler into a library. Main program is now in src/programs/gf.hs

The module src/compiler/GF.hs now serves as a prelimiary compiler API. It just
exports a selection of functions and types from the compiler.

Haddock documentation can be generated with

	cabal haddock --hyperlink-source

Also bumbed the version number to 3.6.10.

src/compiler/GF/Main.hs

@@ -0,0 +1,48 @@
+-- | GF main program (grammar compiler, interactive shell, http server)
+module GF.Main where
+import GF.Compiler
+import GF.Interactive
+import GF.Data.ErrM
+import GF.Infra.Option
+import GF.Infra.UseIO
+import GF.Infra.BuildInfo (buildInfo)
+import Paths_gf
+
+import Data.Version
+import System.Directory
+import System.Environment (getArgs)
+import System.Exit
+import GF.System.Console (setConsoleEncoding)
+
+-- | Run the GF main program, taking arguments from the command line.
+-- (It calls 'setConsoleEncoding' and 'getOptions', then 'mainOpts'.)
+-- Run @gf --help@ for usage info.
+main :: IO ()
+main = do
+  setConsoleEncoding
+  uncurry mainOpts =<< getOptions
+
+-- | Get and parse GF command line arguments. Fix relative paths.
+getOptions = do
+  args <- getArgs
+  case parseOptions args of
+    Ok (opts,files) -> do curr_dir <- getCurrentDirectory
+                          lib_dir  <- getLibraryDirectory opts
+                          return (fixRelativeLibPaths curr_dir lib_dir opts, files)
+    Bad err         -> do ePutStrLn err
+                          ePutStrLn "You may want to try --help."
+                          exitFailure
+
+
+-- | Run the GF main program with the given options and files. Depending on
+-- the options it invokes 'mainGFC', 'mainGFI', 'mainRunGFI', 'mainServerGFI',
+-- or it just prints version/usage info.
+mainOpts :: Options -> [FilePath] -> IO ()
+mainOpts opts files = 
+    case flag optMode opts of
+      ModeVersion     -> putStrLn $ "Grammatical Framework (GF) version " ++ showVersion version ++ "\n" ++ buildInfo
+      ModeHelp        -> putStrLn helpMessage
+      ModeInteractive -> mainGFI opts files
+      ModeRun         -> mainRunGFI opts files
+      ModeServer port -> mainServerGFI opts port files
+      ModeCompiler    -> mainGFC opts files