Added documentation for debugging with core files

[DavidPfander-UniStuttgart]

Added a small paragraph to document signal and exception disable switch of the build system. And more general, how to debug an hpx application with the help of a core file.

I'm pretty sure I didn't put that into a file where it really makes sense, I'm creating this pull request to get the process started.

(Also, Circle CI will likely complain, I couldn't get the documentation creation set up on my system.)

[hkaiser]

(Also, Circle CI will likely complain, I couldn't get the documentation creation set up on my system.)

@DavidPfander-UniStuttgart what didn't work? it should be relatively pain free to set up. Did you see this: http://stellar-group.github.io/hpx/docs/html/hpx/manual/build_system/building_hpx/doc_tools.html?

[DavidPfander-UniStuttgart]

The build system told me that everything is fine, cmake ran successfully. But when I did the make docs, I got strange errors.

Beginning of the error log:

pfandedd@pcsgs09:~/git/hpx/build$ make docs
Generating BoostBook XML file hpx.xml from hpx.qbk.
Generating Output File: hpx.xml
/home/pfandedd/git/hpx/docs/hpx.qbk: warning: Quickbook 1.7 is still under development and is likely to change in the future.
/home/pfandedd/git/hpx/docs/manual/lcos.qbk:204: warning: line breaks generate invalid boostbook (will only note first occurrence).
Generating hpx.dbk
file://usr/share/xml/docbook/schema/dtd/4.2/dbcentx.mod:308: warning: failed to load external entity "file://usr/usr/share/xml/entities/xml-iso-entities-8879.1986/ISOamsa.ent"
%ISOamsa;
         ^
Entity: line 1: 
 %ISOamsa; 
          ^
file://usr/share/xml/docbook/schema/dtd/4.2/dbcentx.mod:312: warning: failed to load external entity "file://usr/usr/share/xml/entities/xml-iso-entities-8879.1986/ISOamsb.ent"
%ISOamsb;
         ^
Entity: line 1: 

(a lot of similar errors)
Later on:

I/O error : No such file or directory
I/O error : No such file or directory
runtime error: file file://usr/share/xml/docbook/stylesheet/docbook-xsl/html/chunker.xsl line 239 element document
xsltDocumentElem: unable to save to file://home/pfandedd/git/hpx/build/share/hpx-1.0.0/docs/html/hpx/preface.html

(Again, lots of similar errors)

I had to built auto-index and quickbook myself and specified them as mentioned in the hpx documentation. I installed the other dependencies from the ubuntu repositories.

[hkaiser]

Well, if it says 'No such file or directory', it's probably missing a file or directory ;-)