Change the name of the folder.

* From sco to Single_Core_Optimization.
* Update Calendar.md.
Edit Single_Core_Optimization.md.

* Use gettimeofday for timing.
* Add makefile.
* Change formatting, correct typos for some parts of the text.
* Add a couple of comments.
Add Cache_Optimization.md.

* Introduction, history and types of programs.
Add more test to Cache_Optimization.md.

* Memory hierarchy, cache, hits and misses.
* Cache optimization.
* Array access and matrix-matrix multiplication.
* MMM code - naive and blocked.
Add stuff about double-dimensional arrays.