Remove `Columns` class; do the work in `DataSpec`

README.md

@@ -9,7 +9,7 @@ width.
 ```py
 import math
 import sys
-from asccol import DataSpec, Columns, parse_data
+import asccol
 
 def simple_time(s):
     """Convert a HHMM string to an (H, M) tuple."""
@@ -24,9 +24,9 @@ def filtered_float(s):
 
 # 10 minute data
 # See https://amrc.ssec.wisc.edu/data/ftp/pub/aws/q10/q10readme.txt
-Q10 = DataSpec(
+Q10 = asccol.DataSpec(
     leading=2,  # lines to delete
-    cols=Columns(
+    cols=(
         ('year', int, 4),  # keyword, type (converter function), width
         ('jdate', int, 4),
         ('month', int, 3),
@@ -41,7 +41,7 @@ Q10 = DataSpec(
     ),
 )
 
-for row in parse_data(sys.stdin, Q10):
+for row in asccol.parse_data(sys.stdin, Q10):
     print(row)
 ```
 

asccol.py

@@ -6,31 +6,14 @@ Column = namedtuple('Column', ('name', 'type', 'width'))
 
 
 class DataSpec:
-    """Details about how to parse an aligned data file.
-
-    Arguments:
-        cols (Columns): columns' name, type, and width
-        leading (int): number of leading lines to ignore
-    """
+    """Details about how to parse an aligned data file."""
 
     def __init__(self, cols, leading=0):
-        self.cols = cols
+        self.cols = tuple(map(Column._make, cols))
         self.leading = leading
         self.namedtuple = namedtuple('row', (col.name for col in cols))
 
 
-class Columns(tuple):
-    """Details about how to parse aligned data."""
-
-    def __new__(cls, *data):
-        columns = map(Column._make, data)
-        return tuple.__new__(cls, columns)
-
-    def __repr__(self):
-        contents = ', '.join(map(repr, self))
-        return f'{type(self).__name__}({contents})'
-
-
 def parse_data(stream, dataspec):
     """Read lines from `stream` and yield `namedtuple` data."""
     for line_num, line in enumerate(stream, start=1):