Add multiplatform opalkelly SDK files, got mac working, committing so…

… i can work on linux

miniscope_io/vendor/opalkelly/README.md

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+# OpalKelly FPGA SDK
+
+See documentation here: https://docs.opalkelly.com/fpsdk/frontpanel-api/programming-languages/
+
+## Files
+
+The Python API distribution includes the files listed below:
+
+- `ok.py`
+- `_ok.pyd` – Windows, architecture-specific for 32-bit/64-bit
+- `_ok.so` – Linux, Mac OS, architecture-specific for 32-bit/64-bit
+- `okFrontPanel.dll` – Windows, architecture-specific for 32-bit/64-bit
+- `libokFrontPanel.so` – Linux, Mac OS, architecture-specific for 32-bit/64-bit
+- `okimpl_fpoip.dll` – (optional) Windows, architecture-specifc DLL used to provide FPoIP functionality
+- `okimpl_fpoip.so` – (optional) Linux, architecture-specifc DLL used to provide FPoIP functionality
+
+## Changes
+
+### Mac
+
+The documentation suggests that all one needs to do is add the folders to
+`DYLD_LIBRARY_PATH`, but unfortunately that doesn't work because they have hard-coded
+the location to search for the dylib as `@rpath/libokFrontPanel.dylib` and 
+then set `rpath` to some weird directory on their build server.
+
+So instead we modify the import location in `_ok.so` like:
+
+```bash
+install_name_tool -change \
+  @rpath/libokFrontPanel.dylib \
+  @loader_path/libokFrontPanel.dylib \
+  miniscope_io/vendor/opalkelly/mac/_ok.so
+```

miniscope_io/vendor/opalkelly/__init__.py

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+import pdb
+import sys
+from pathlib import Path
+import os
+import subprocess
+
+def patch_env_path(name:str, value:str):
+    val = os.environ.get(name, None)
+    if val is None:
+        val = value
+    else:
+        val = ':'.join([val, value])
+    os.environ[name] = val
+
+base_path = Path(__file__).parent.resolve()
+if sys.platform == 'darwin':
+    from miniscope_io.vendor.opalkelly.mac.ok import *
+
+elif sys.platform.startswith('linux'):
+    # Linux
+    pass
+elif sys.platform.startswith('win'):
+    # Windows
+    pass
+else:
+    raise ImportError('Dont know what operating system you are on, cant use OpalKelly')