Update vowpal_wabbit submodule (VowpalWabbit#37)

* Update vowpal_wabbit submodule

* Pulls in these fixes
- fac3c06 ("Fix crash when empty multi_ex is supplied for --cb_explore_adf (VowpalWabbit#1679)")
- f085178 ("bugfix:  cb_adf is not including some examples in stats calculation (VowpalWabbit#1686)")
- c9d9af7 ("Fix memory leak in cb_explore_adf (VowpalWabbit#1698)")
- 1e8742b ("Fix some VW initialization memory leaks (VowpalWabbit#1697)")
- 75423e3 ("Fix best constant and best constant's loss calculation when using ksvm (VowpalWabbit#1704)")
- 2b64c3c ("Use std::exp instead of exp free function (VowpalWabbit#1709)")
- 6b7b160 ("Fix unused params warnings plus incomplete struct init (done to default values). (VowpalWabbit#1710)")
- 2e1602d ("Compile fixes (VowpalWabbit#1713)")
- b50fb59 ("Make cbify reduction respect is_learn parameter (VowpalWabbit#1722)")

This also includes the option parsing changes
- b8ab396 ("`options_i` command line parsing refactor  (VowpalWabbit#1706)"
- 5b020c4 ("Ataymano/mac options types fix (VowpalWabbit#1718)")

There are other small or non-rl-consumable changes

* Enable injection of msbuild path in Windows command-line build

* Update vowpal_wabbit submodule

* This pulls in the additional fix made to address the bug discovered in
  the previous attempt to update this.

  Fixed in VowpalWabbit#1742

* Updates safe_vw.cc to get rid of a no-longer-necessary cleanup step

build-windows.cmd

@@ -5,14 +5,16 @@ for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio
   set InstallDir=%%i
 )
 
-if not exist "%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" (
-  echo ERROR: MsBuild couldn't be found
-  exit /b 1
-)
-
-if not defined VcpkgInstallRoot (
-  echo ERROR: VcpkgInstallRoot must be set
-  exit /b 1
+REM Enable injecting of msbuild path (rather than relying on an installed version of Visual Studio),
+REM but fallback to detection path if not provided.
+if not defined msBuildPath (
+  if not exist "%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" (
+    echo ERROR: MsBuild couldn't be found
+    exit /b 1
+  )
+  else (
+    SET "msBuildPath=%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe"
+  )
 )
 
 call "%InstallDir%\Common7\Tools\VsDevCmd.bat"
@@ -30,7 +32,6 @@ nuget install -o packages bindings\cs\rl.net.native\packages.config
 nuget install -o packages rlclientlib\packages.config
 nuget install -o packages unit_tests\packages.config
 
-
 dotnet restore rl.sln
 
 "%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" "rl.sln" /m /verbosity:normal /p:Configuration=Release;Platform=x64

rlclientlib/vw_model/safe_vw.cc

@@ -3,6 +3,7 @@
 // VW headers
 #include "example.h"
 #include "parse_example_json.h"
+#include "parser.h"
 
 namespace reinforcement_learning {
 
@@ -85,7 +86,6 @@ namespace reinforcement_learning {
 
     // cleanup VW instance
     reset_source(*_vw, _vw->num_bits);
-    release_parser_datastructures(*_vw);
 
     VW::finish(*_vw);
   }