add cmake support and .gitignore file

.gitignore

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+.cache
+build
+.vscode

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+project(pico)
+
+option(PICO_TEST "build test" OFF)
+option(PICO_EXAMPLE "build example" OFF)
+
+if(PICO_TEST)
+    add_subdirectory(test)
+endif()
+
+if(PICO_EXAMPLE)
+    add_subdirectory(example)
+endif()
+
+add_library(${PROJECT_NAME} INTERFACE)
+target_include_directories(${PROJECT_NAME} INTERFACE ${CMAKE_SOURCE_DIR})

example/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+
+add_executable(hasher hasher.cpp)
+target_include_directories(hasher
+    PRIVATE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>)
+add_executable(interactive_hasher interactive_hasher.cpp)
+target_include_directories(interactive_hasher
+    PRIVATE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>)

test/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+
+include(CTest)
+
+add_executable(unittest)
+
+target_sources(unittest PRIVATE test.cpp)
+
+target_include_directories(unittest
+    PRIVATE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>)
+
+add_test(NAME unittest COMMAND unittest)