preprocess.md

+Code preprocess_refact.py, git revision  ec4a87cb
+
+- Get input, client RESIF, jday +/- 1 min
+- No interpolation, assume that trace is already 200Hz and starts at `00:00:00.000000 +/- n * 1./200`
+- Cut the trace(s) between 00:00:00.000000 and 23:59:59.995000
+- Fill eventual gaps with zeroes
+- Butterworth Bandpass Filter between 0.01 and 30.0 Hz, order 4
+- write h5 datasets, as :
+
+```
+> h5ls -rv FR.OGS1.00.HHZ.trace.int8.h5
+Opened "FR.OGS1.00.HHZ.trace.int8.h5" with sec2 driver.
+/                        Group
+    Location:  1:96
+    Links:     1
+/2013                    Group
+    Location:  1:130890
+    Links:     1
+/2013/001\               Dataset {17280000/17280000}
+    Location:  1:800
+    Links:     1
+    Chunks:    {16875} 67500 bytes
+    Storage:   69120000 logical bytes, 91314 allocated bytes, 75694.86% utilization
+    Filter-0:  deflate-1 OPT {6}
+    Type:      native int
+[...]
+```
+