[modernize] Fix StringTo... casing, duplicate declaration, and internal header guard

- Correct casing of StringToLoggingType and StringToDumpFormatType for
  consistency with the rest of the API.
- Fix a bug in include/ceres/types.h where StringToDumpFormatType was
  incorrectly declared with a LoggingType* argument.
- Update the header guard in internal/ceres/problem_impl.h to use the
  CERES_INTERNAL_ prefix instead of CERES_PUBLIC_.

Change-Id: Ia28c01e368e839043251594e0b11ba1c17ee4483

include/ceres/types.h

diff --git a/include/ceres/types.h b/include/ceres/types.h
index 4b4f16a..f677d43 100644
--- a/include/ceres/types.h
+++ b/include/ceres/types.h
@@ -543,12 +543,11 @@
                                                 NumericDiffMethodType* type);
 
 CERES_EXPORT const char* LoggingTypeToString(LoggingType type);
-CERES_EXPORT bool StringtoLoggingType(std::string value, LoggingType* type);
+CERES_EXPORT bool StringToLoggingType(std::string value, LoggingType* type);
 
 CERES_EXPORT const char* DumpFormatTypeToString(DumpFormatType type);
-CERES_EXPORT bool StringtoDumpFormatType(std::string value,
+CERES_EXPORT bool StringToDumpFormatType(std::string value,
                                          DumpFormatType* type);
-CERES_EXPORT bool StringtoDumpFormatType(std::string value, LoggingType* type);
 
 CERES_EXPORT const char* TerminationTypeToString(TerminationType type);
 

internal/ceres/problem_impl.h

diff --git a/internal/ceres/problem_impl.h b/internal/ceres/problem_impl.h
index 0932468..c366f0e 100644
--- a/internal/ceres/problem_impl.h
+++ b/internal/ceres/problem_impl.h
@@ -36,8 +36,8 @@
 // to always put a Problem object into a scoped pointer; this needlessly muddies
 // client code for little benefit. Therefore, the PIMPL comprise was chosen.
 
-#ifndef CERES_PUBLIC_PROBLEM_IMPL_H_
-#define CERES_PUBLIC_PROBLEM_IMPL_H_
+#ifndef CERES_INTERNAL_PROBLEM_IMPL_H_
+#define CERES_INTERNAL_PROBLEM_IMPL_H_
 
 #include <array>
 #include <map>
@@ -225,4 +225,4 @@
 
 #include "ceres/internal/reenable_warnings.h"
 
-#endif  // CERES_PUBLIC_PROBLEM_IMPL_H_
+#endif  // CERES_INTERNAL_PROBLEM_IMPL_H_

internal/ceres/types.cc

diff --git a/internal/ceres/types.cc b/internal/ceres/types.cc
index 4bbd602..dc75a1c 100644
--- a/internal/ceres/types.cc
+++ b/internal/ceres/types.cc
@@ -361,7 +361,7 @@
   }
 }
 
-bool StringtoLoggingType(std::string value, LoggingType* type) {
+bool StringToLoggingType(std::string value, LoggingType* type) {
   UpperCase(&value);
   STRENUM(SILENT);
   STRENUM(PER_MINIMIZER_ITERATION);
@@ -377,7 +377,7 @@
   }
 }
 
-bool StringtoDumpFormatType(std::string value, DumpFormatType* type) {
+bool StringToDumpFormatType(std::string value, DumpFormatType* type) {
   UpperCase(&value);
   STRENUM(CONSOLE);
   STRENUM(TEXTFILE);