Overhaul for speed and robustness

Significant overhauling, deduplicating, robustness improvement for RINEX and CRINEX reading.
Particular improvements for:

• CRINEX 1.x files
• uncompressed and compressed OBS 2.x files

In particular, the speed difference between "slow" and "fast" reading of OBS2 files is now less than 10% and memory usage is reduced proportional to tlim if specified.

Please let us know of any problem RINEX files.