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_octal.py

@@ -0,0 +1,38 @@
+"""Convert a Decimal Number to an Octal Number."""
+
+import math
+
+# Modified from:
+# https://github.com/TheAlgorithms/Javascript/blob/master/Conversions/DecimalToOctal.js
+
+
+def decimal_to_octal(num):
+    """Convert a Decimal Number to an Octal Number."""
+    octal = 0
+    counter = 0
+    while num > 0:
+        remainder = num % 8
+        octal = octal + (remainder * math.pow(10, counter))
+        counter += 1
+        num = math.floor(num / 8)  # basically /= 8 without remainder if any
+        # This formatting removes trailing '.0' from `octal`.
+    return'{0:g}'.format(float(octal))
+
+
+def main():
+    """Print octal equivelents of decimal numbers."""
+    print("\n2 in octal is:")
+    print(decimal_to_octal(2))  # = 2
+    print("\n8 in octal is:")
+    print(decimal_to_octal(8))  # = 10
+    print("\n65 in octal is:")
+    print(decimal_to_octal(65))  # = 101
+    print("\n216 in octal is:")
+    print(decimal_to_octal(216))  # = 330
+    print("\n512 in octal is:")
+    print(decimal_to_octal(512))  # = 1000
+    print("\n")
+
+
+if __name__ == '__main__':
+    main()