missing MAX_SEN_LEN and EPOCH

[luckystar1992]

Compare to the original C code released by Google, MAX_SEN_LEN and EPOCH is missing, which caused these two problem.

[1] In the sub training process, each process read lines from file start and end. Once the input file contains only the one line (for example text8 corpus), following code snippets would caused bug.

 while fi.tell() < end:
        line = fi.readline().strip()
        # Skip blank lines
        if not line:
            continue

line = fi.readline().strip() would load the whole tokens from start.

[2] EPOCH would create embedding with more training samples.