wip: custom environment variable passing

You should be able to tell your sci deployment which env vars should be
passed to the pipelines with -e ENV1 -e ENV2 and so on

include/strlist.h

@@ -0,0 +1,51 @@
+/**
+ * sci - a simple ci system
+   Copyright (C) 2024 Asger Gitz-Johansen
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+#ifndef SCI_STRLIST_H
+#define SCI_STRLIST_H
+
+// doubly linked list
+typedef struct strlist_node {
+    char* str;
+    struct strlist_node* previous;
+    struct strlist_node* next;
+} strlist_node;
+
+// Create a new root node.
+// This function is not threadsafe.
+strlist_node* create_strlist_node(char* str);
+
+// Add a new string to the string list.
+// This function is not threadsafe.
+strlist_node* add_str(char* str, strlist_node* root);
+
+// add a new string list node to the list.
+// This function is not threadsafe.
+strlist_node* add_str_node(strlist_node* str_node, strlist_node* root);
+
+// Remove a string list node from the list.
+// This will free the str and stitch the "previous" and "next" ptrs.
+// This function is not threadsafe.
+void remove_strlist_node(strlist_node* node);
+
+// Completely clear the list.
+// The list is completely invalid after this call and should be discarded.
+// root itself will not be free'd by this function, but all content will be.
+// This function is not threadsafe.
+void clear_strlist(strlist_node* root);
+
+#endif