csvcat: concatenate CSVs with the same shape

[Notgnoshi]

• Must have the same number of columns
  • With special handling for the index column
• Data will be untransformed
• CSVs will be concatenated in the order of CLI arguments
• Option to add an --index-name column that enumerates which CSV the data came from
  • Option: CSV filename
  • Option: 0-based index
  • Option: 1-based index
  • Option: UUID

Example 1 - concatenate 2 CSVs

file 1:

v1	v2
0.5	a
-2	b

file 2:

v1	v2
0.1	c
5	d

output:

index	v1	v2
0	0.5	a
0	-2	b
1	0.1	c
2	5	d

Example 2 - concatenate another CSV to an existing series

file 1:

index	v1	v2
0	0.5	a
1	-2	b
2	-0.1	c

file 2:

v1	v2
0.1	c
5	d

output:

index	v1	v2
0	0.5	a
1	-2	b
2	-0.1	c
3	0.1	c
3	5	d