Use sub-namespaces for functionality-groups.

src/main.cpp

@@ -46,7 +46,7 @@ int main(int argc, char *argv[])
     po::variables_map vm;
     try
     {
-        vm = epubgrep::parse_options(argc, argv);
+        vm = epubgrep::options::parse_options(argc, argv);
     }
     catch (std::exception &e)
     { // Exceptions we can't recover from or ones we don't know.

src/options.cpp

@@ -31,7 +31,7 @@
 #include <iostream>
 #include <string>
 
-namespace epubgrep
+namespace epubgrep::options
 {
 
 namespace po = boost::program_options;
@@ -129,4 +129,4 @@ fs::path get_config_path()
     return "epubgrep.conf";
 }
 
-} // namespace epubgrep
+} // namespace epubgrep::options

src/options.hpp

@@ -21,7 +21,7 @@
 
 #include <boost/program_options/variables_map.hpp>
 
-namespace epubgrep
+namespace epubgrep::options
 {
 
 namespace po = boost::program_options;
@@ -38,6 +38,6 @@ po::variables_map parse_options(int argc, char *argv[]);
  */
 fs::path get_config_path();
 
-} // namespace epubgrep
+} // namespace epubgrep::options
 
 #endif // EPUBGREP_OPTIONS_HPP