Implement loadtxt and savetxt

This also includes a minimal CMake build system. We can improve the
build system in further PRs.

Fixes fortran-lang#16.

CMakeLists.txt

@@ -0,0 +1,9 @@
+cmake_minimum_required(VERSION 3.5.0 FATAL_ERROR)
+
+enable_language(Fortran)
+
+project(stdlib)
+
+enable_testing()
+
+add_subdirectory(src)

src/CMakeLists.txt

@@ -0,0 +1,12 @@
+set(SRC
+    stdlib_types.f90
+    stdlib_io.f90
+)
+
+add_library(fortran_stdlib ${SRC})
+
+install(TARGETS fortran_stdlib
+        RUNTIME DESTINATION bin
+        ARCHIVE DESTINATION lib
+        LIBRARY DESTINATION lib
+    )

src/stdlib_io.f90

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+module stdlib_io
+use stdlib_types
+implicit none
+private
+public loadtxt, savetxt
+
+contains
+
+subroutine loadtxt(filename, d)
+! Loads a 2D array from a text file.
+!
+! Arguments
+! ---------
+!
+! Filename to load the array from
+character(len=*), intent(in) :: filename
+! The array 'd' will be automatically allocated with the correct dimensions
+real(dp), allocatable, intent(out) :: d(:, :)
+!
+! Example
+! -------
+!
+! real(dp), allocatable :: data(:, :)
+! call loadtxt("log.txt", data)  ! 'data' will be automatically allocated
+!
+! Where 'log.txt' contains for example::
+!
+!     1 2 3
+!     2 4 6
+!     8 9 10
+!     11 12 13
+!     ...
+!
+character :: c
+integer :: s, ncol, nrow, ios, i
+logical :: lastwhite
+real(dp) :: r
+
+open(newunit=s, file=filename, status="old")
+
+! determine number of columns
+ncol = 0
+lastwhite = .true.
+do
+   read(s, '(a)', advance='no', iostat=ios) c
+   if (ios /= 0) exit
+   if (lastwhite .and. .not. whitechar(c)) ncol = ncol + 1
+   lastwhite = whitechar(c)
+end do
+
+rewind(s)
+
+! determine number or rows
+nrow = 0
+do
+   read(s, *, iostat=ios) r
+   if (ios /= 0) exit
+   nrow = nrow + 1
+end do
+
+rewind(s)
+
+allocate(d(nrow, ncol))
+do i = 1, nrow
+    read(s, *) d(i, :)
+end do
+close(s)
+end subroutine
+
+subroutine savetxt(filename, d)
+! Saves a 2D array into a textfile.
+!
+! Arguments
+! ---------
+!
+character(len=*), intent(in) :: filename  ! File to save the array to
+real(dp), intent(in) :: d(:, :)           ! The 2D array to save
+!
+! Example
+! -------
+!
+! real(dp) :: data(3, 2)
+! call savetxt("log.txt", data)
+
+integer :: s, i
+open(newunit=s, file=filename, status="replace")
+do i = 1, size(d, 1)
+    write(s, *) d(i, :)
+end do
+close(s)
+end subroutine
+
+
+logical function whitechar(char) ! white character
+! returns .true. if char is space (32) or tab (9), .false. otherwise
+character, intent(in) :: char
+if (iachar(char) == 32 .or. iachar(char) == 9) then
+    whitechar = .true.
+else
+    whitechar = .false.
+end if
+end function
+
+end module

src/stdlib_types.f90

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+module stdlib_types
+implicit none
+private
+public sp, dp, qp
+
+integer, parameter :: sp=kind(0.), &             ! single precision
+                      dp=kind(0.d0), &           ! double precision
+                      qp=selected_real_kind(32)  ! quadruple precision
+
+end module