Add single threaded implementation.

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#	new file:   src/main/java/com/github/acme/learning/threading/FibonacciComputerSingleThread.java
#	new file:   src/test/java/com/github/acme/learning/threading/FibonacciComputerSingleThreadTest.java
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Added new tests for base cases of fibonacci.
Added MultiThreadWithOverhead implementation.