Update Colvars to version 2017-10-11

Notable features are the umbrella-integration based free energy estimator for
eABF, and the traditional thermodynamic integration estimator now available
for umbrella sampling, SMD, metadynamics.  Also included are several small fixes.

Below is a list of relevant commits in the Colvars repository since the last update.

321d06a 2017-10-10 Add macros to manage colvarscript commands [Giacomo Fiorin]
26c3bec 2017-10-09 Document coming availability of Lepton in LAMMPS [Giacomo Fiorin]
cc8f249 2017-10-04 Clarify that SMP depends on code build [Giacomo Fiorin]
0b2ffac 2017-10-04 Summarize colvar definition options, clarify some details [Giacomo Fiorin]
28002e0 2017-10-01 Separate writing of restart file from other output (e.g. PMFs) [Giacomo Fiorin]
92f7c1d 2017-10-01 Deprecate colvarsTrajAppend [Giacomo Fiorin]
12a707f 2017-09-26 Accurate Jacobian calculation for RMSD variants [Jérôme Hénin]
fe389c9 2017-09-21 Allow subtractAppliedForce with extended-L again [Jérôme Hénin]
c050ce0 2017-09-18 Silence compiler warnings, remove Tabs [Giacomo Fiorin]
cb41905 2017-01-11 Add base class for TI estimator in other biases than ABF [Giacomo Fiorin]
a1bc676 2017-09-14 Avoid writing to unopened traj file [Jérôme Hénin]
b58d8cd 2017-09-08 Function to check for overlapping groups [Jérôme Hénin]
1e5efec 2017-09-07 Check for overlapping groups in coordNum [Jérôme Hénin]
03a61a4 2017-04-06 Add UI-based estimator [fhh2626]
ae43754 2017-08-17 Fix outputCenters parsing [Josh Vermaas]
1619e0e 2017-08-14 Delete static feature arrays in cvm destructor [Jérôme Hénin]