Implement Three New Algorithms (#948)

* Create average_median.py

I created a program to calculate the median of a list of numbers.

* Changed Odd to Even in String

* Create decimal_to_binary.py

- Added 'conversions' folder.
- Created a decimal to binary converter.

* Implemented Decimal to Octal Algorithm

- I created a decimal to octal converter based on the converter in the TheAlgorithms/Python project.
- I added two newlines to make the output of decimal_to_binary.py better.

conversions/decimal_to_binary.py

@@ -0,0 +1,25 @@
+"""Convert a Decimal Number to a Binary Number."""
+
+
+def decimal_to_binary(num):
+    """Convert a Decimal Number to a Binary Number."""
+    binary = []
+    while num > 0:
+        binary.insert(0, num % 2)
+        num >>= 1
+    return "".join(str(e) for e in binary)
+
+
+def main():
+    """Print binary equivelents of decimal numbers."""
+    print("\n2 in binary is:")
+    print(decimal_to_binary(2))  # = 10
+    print("\n7 in binary is:")
+    print(decimal_to_binary(7))  # = 111
+    print("\n35 in binary is:")
+    print(decimal_to_binary(35))  # = 100011
+    print("\n")
+
+
+if __name__ == '__main__':
+    main()