Pyntcloud.from_file for multiple files?

Perhaps this is a rare use-case, but I often have folders full of .ply files to load into one cloud. I am currently manually reading them in (just points, probably adding mesh and other structures is much harder), but it could be helpful to have a feature for this built-in (or an easy way to concatenate two Pyntcloud objects?)

```
from pyntcloud.io import read_ply

last_df = None
for c_file in all_files:
cur_df = read_ply(c_file)['points']
if last_df is None:
last_df = cur_df
else:
last_df = pd.concat([last_df, cur_df])
```