adding-write-velocity-or-displacement-history-option

[odakan]

@volkanozsarac

Modify the write method of EzGM.selection:

1) add rtype option 2) write documentation for rtype 3) implement get_history() local method 4) integrate acc. series dir. 1 and 2 just after scaling and before writing to txt

_gethistory(series, dt, type): Cumulatively integrates "series" over [0, t] with "dt" to obtain "type".

Comparison between EzGM and SeismoSignal:

[odakan]

@volkanozsarac, it looks great!

Everything seems to work fine. Also, I think it is a good idea to save scaling factors as .txt.

Kudos! Deniz