support env variables for -t and -H

[shenwei356]

No description provided.

[shenwei356]

Available in v0.13.0-dev2 or later versions. Examples:

$ cat digitals.tsv 
4       5       6
1       2       3
7       8       0
8       1,000   4

$ cat digitals.tsv | csvtk head -n 3 -H -t | csvtk cut -f 2,1 -H -t
5       4
2       1
8       7

$ export CSVTK_T=1; 
$ export CSVTK_H=true;
$ cat digitals.tsv | csvtk head -n 3 | csvtk cut -f 2,1
5       4
2       1
8       7

[shenwei356]

Available in v0.13.0 and later versions