input: Write a function that takes two strings and returns true if the first string is a subsequence of the second. The function should return false otherwise. A subsequence means that the characters of the first string appear in the second string in the same order, but not necessarily consecutively.
  
  def is_subsequence(str1, str2):
      i = 0
      j = 0
  
      while(i < len(str1) and j < len(str2)):
          if str1[i] == str2[j]:
              i += 1
          j += 1
  
      return i == len(str1)
  
  assert is_subsequence("abc", "qaxbcy")==True
  assert is_subsequence("abc", "qaxbyc")==True
  assert is_subsequence("abc", "qaxbydc")==False
  assert is_subsequence("abc", "acxbyd")==False
  assert is_subsequence("", "qaxbydc")==True
output: def is_subsequence(str1, str2):
      i = 0
      j = 0
  
      while(i < len(str1) and j < len(str2)):
          if str1[i] == str2[j]:
              i += 1
          j += 1
  
      return i == len(str1)