Code Clean-up: Move include of SimpleIni.h form ETISS.h to ETISS.cpp

[CFoik]

Moving include of external dependency header SimpleIni form ETISS.h to ETISS.cpp where it is actually required.
This allows external programs to use ETISS.h without re-importing SimpleIni.

[github-actions]

Performance Statistics

Status for the gcc Just-In-Time Engine (for commit 653e2ab): No significant performance change
Current dhrystone MIPS for gcc JIT : 96.7
Previous best for gcc JIT (recorded in commit 4d2d26f): 108.31, difference -10.72%

Status for the llvm Just-In-Time Engine (for commit 653e2ab): Regressed since commit 78716e7
Current dhrystone MIPS for llvm JIT : 25.99
Previous best for llvm JIT (recorded in commit 940dbdd): 36.11, difference -28.03%

Status for the tcc Just-In-Time Engine (for commit 653e2ab): 🥇 New best performance!
Current dhrystone MIPS for tcc JIT : 58.33
Previous best for tcc JIT (recorded in commit 653e2ab): 58.33, difference 0.08%

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[JoGei]

Good intention and way forward in cleaning up sources.

Problem is that headers are cluttered with includes that are not needed in the including header.

Some additions that I made:

I have introduced SimpleIni as a CMake object library target (no linking of simpleini.a) with public headers that will be installed alongside etiss headers.