Opts: Make singleton; senseApi: check senseApiLibPath, get senseApiDescFn pointer.

* OptionsParser now has a singleton.
* We now use the cmdline opt -p <senseApiLibPath>, and search for
  the specified library in:
  * senseApiLibPath, then CWD, then the place where our executable
    is running from, and then finally we let the hosting OS do
    its own search.
* We now call dlsym() on dlopen()'d libs to to get the senseApiDescFn
  pointer.

hcore/include/senseApis/senseApiLib.h

@@ -39,7 +39,7 @@ public:
 class SenseApiLib
 {
 public:
-    typedef const CSenseApiDesc *(SenseApiDescGetterFn)(void);
+    typedef const CSenseApiDesc* (SenseApiDescGetterFn)(void);
 
 public:
     SenseApiLib(const std::string& path)
@@ -58,7 +58,7 @@ public:
      * This getter function should be visible to dlsym() so that Harikoff can
      * find it in the lib after loading it, and call it.
      */
-    SenseApiDescGetterFn *getSenseApiDescriptor;
+    std::function<SenseApiDescGetterFn> getSenseApiDescriptor;
 
     /**
      * @brief Harikoff will call the `getSenseApiDescriptor` getter function and