Clean up singleton implementation

Move the singleton instances into their namespaces, and use
get()/getInstance() for uniform accesses.

Review-Url: https://codereview.chromium.org/2154843002
diff --git a/fpdfsdk/fpdfview.cpp b/fpdfsdk/fpdfview.cpp
index 34e7d23..f47de15 100644
--- a/fpdfsdk/fpdfview.cpp
+++ b/fpdfsdk/fpdfview.cpp
@@ -262,8 +262,8 @@
 FPDF_InitLibraryWithConfig(const FPDF_LIBRARY_CONFIG* cfg) {
   g_pCodecModule = new CCodec_ModuleMgr();
 
-  CFX_GEModule::Create(cfg ? cfg->m_pUserFontPaths : nullptr, g_pCodecModule);
-  CPDF_ModuleMgr::Create();
+  CFX_GEModule* pModule = CFX_GEModule::Get();
+  pModule->Init(cfg ? cfg->m_pUserFontPaths : nullptr, g_pCodecModule);
   CPDF_ModuleMgr* pModuleMgr = CPDF_ModuleMgr::Get();
   pModuleMgr->SetCodecModule(g_pCodecModule);
   pModuleMgr->InitPageModule();