Merge branch '40-the-build-system-does-not-set-library-flags-of-libxml2-and-gsl-for-pkg-config' into 'develop'

Resolve "The build system does not set library flags of LibXML2 and GSL for pkg-config"

Closes #40

See merge request !31

Bump version number.

See merge request !33

Resolve "nelvalence should always be set"

Closes #32

See merge request !32

Release 0.2.3

See merge request !28

Add missing public declaration.

See merge request !27

Add a getter for the wavefunction in pspio_state.

See merge request !26

[ci] initial commit

See merge request !25

Resolve "Relicense under MPLv2"

Closes #26

See merge request !24

Sync master

Closes #30, #31, #33, and #35

See merge request !23

Installing a pkg-config file

See merge request !22

Function _get_symbol() in Fortran return garbage, fixes #30

See merge request !17

Correct string comparison in symbol_to_z(), fixes #31.

See merge request !18

Add assertion on index when accessing array elements, fixes #33.

See merge request !19

Use proper ordering when calling projector copy from Fortran, fixes #35.

See merge request !20

Imported the AX_PTHREAD M4 macro into the build system

See merge request !21

Travis

See merge request !16