Removed all examples mentioning matheval

I removed matheval everywhere in the code. Now, MATHEVAL
(and CUSTOM) keywords are automatically using lepton (see #244).

Notice that env var PLUMED_USE_LEPTON is now ignored.

closes #244

Notice that Lepton is always available but should be triggered with
export PLUMED_USE_LEPTON=yes

Also notice that to behave as matheval it requires defining a pi variable.

[makedoc]

Notice that almost all files were updated with the astyle commit
2813d759

Year in header is here updated to 2017

I replaced
verbatim
endverbatim
with
plumedfile
endplumedfile

in (hopefully) all the places where it was appropriate.

This is a huge commit, applying indentation to the whole
code. Notice that this commit is made on master branch
after having merged with -s ours from branch v2.3

See #215

This is a huge commit, applying indentation to the whole
code.

See #215

I added an example similar to the one that I provided
on the mailing list about how to mimick
POINT_FROM_AXIS and PROJ_ON_AXIS

[makedoc]

[makedoc]

closes #158

added PERIODIC=NO in the example because this keyword is compulsory.

I set it to 2 instead of 2.0, so that it will not be necessary
to update it

Namespaces are used now in bias/colvar/function/cltools

All the source code have been moved into subdirectories of src/
Some of these subdirectories are treated in a special manner:
src/wrapper contains the wrappers for MD codes
src/main contains the main.cpp file
src/config contains files generated without compilation,
  just based on configuration info
src/lib is the place where executables and libraries are put
  at the end
src/cltools contains the command line tools
src/tools contains plumed tools (reusable classes)
src/basic contains PlumedMain, Action hierarchy and other basic stuff
src/multicolvar contains MultiColvar stuff
src/imd is the interactive MD (still not totally portable).

Notice that, to allow easy inclusion of .h files from other modules,
I link all the directories in src/ into module directory. In this
way it is possible e.g. to write #include "config/PlumedConfig.h"

See src/README and src/basic/Makefile to understand how inter-module
dependencies are set

as suggested by Gareth