Fixing some warnings for Visual C++ and also using ostringstream instead of stringstream when appropriate

More size_t fixes (ie trying to be consistent) and a bug was found when spatially interpolating using a few specific algorithms that would not reset their internal vectors between two calls (thanks Matteo for helping uncover this bug!)

In order to implement an efficient and portable object serialization, it has been decided that all serializable objects would be manually serialized to an std::iostream. Then, the parallelization framework (mpi, popc, etc) can take over this stream and move it to another node. Therefore, the operators "<<" and ">>" are now reserved for serialization (as seems to be standard) and the debug outputs are obtained by printing "object.toString()". This means that all debug code has potentially to be fixed, by replacing "std::cout << object" by "std::cout << object.toString()".

The plugins are no longer separately loadable libraries, but are fully incorporated into libmeteoio. All classes and facilities that provided capabilites for the dynamic loading were deleted (DynamicLibrary). IOPlugin now holds a function pointer to an instantiation function for children of IOInterface. In IOHandler::registerPlugins() all plugins need to be registered with the key name, the class name, a pointer to an instance of the class and a function pointer to the instantiation function for the class (child of IOInterface). IOInterface lost some complexity and thus the constructor of the base class does not have to be called in derived classes anymore.

The CMakeLists.txt files had to be updated to no longer make separate dynamically loadable libraries for each plugin, but to simply add the classes the user selectes to the meteoio library. 

As a side effect the io.ini key GENERAL::PLUGINPATH is no longer necessary.

Several 1D statistical methods has been implemented while the existing ones have been made nodata safe.

Added a redefinition of the << operator for IOPlugin and IOHandler. This should be convenient for debugging!

Some small optimizations have been brought into the spatial interpolations following some tests with cachegrind. Nothing huge, but small improvements.

Overall all include statements within in the library have been replaced by angle brackets, the default install path for the include file is $CMAKE_INSTALL_DIR/include/meteoio, the meteoio libraries (static and shared) will be installed in $CMAKE_INSTALL_DIR/lib per default.

The plugins will be installed in the subdirectory $CMAKE_INSTALL_DIR/lib/meteoio/plugins

Then, the remaining namespace issues with doxygen have been fixed, by enclosing the full class implementation in the namespace (as seen for the libstdc++). This removes all these irritating issues. But the popc version has been broken by the change (as seen in LegacyIO).

Changed the name of the Date_IO class to Date. In case of namespace conflicts, just use mio::Date to reference the MeteoIO Date class.

A new slope computation algorithm has bee added: CARD It computes the slope using Corripio and then discretizes the azimuth along 8 cardinal directions and the slope by degrees. This should be all that GEOtop needs for its drainage direction (then simply calling a dem.update("CARDINAL")).

The copyright notices have been put in place in all files (headers and cc) with proper attribution of copyright.

The documentation has been improved, specially fixing issue 22. Warning messages of doxygen have been fixed. An example subdirectory has been created in /doc and contains (currently) 2 examples of code using MeteoIO.

The whole library has been given its new name and several classes have been renamed in order to better match their purpose. The Makefile has been modified accordingly.